Hello! I'm a huge fan of your ideas for quality, and I think they're easily the best ideas/executions for expansions that I've seen. (Good balance of not having bloat, nice stat variation, artstyle which seamlessly matches the base game, very novel concepts, etc).

Since you mentioned you're interested in balancing suggestions, I have a few for both the base mod and the shiny mod. I'll be posting this in the discussions for both mods - I apologize in advance for the yap, just very excited to see these two pop up and figured I'd share my two cents and try to chip in.

I'm not a great programmer, but if you would like art assets and similar, I would love to contribute. I have some ideas for shiny quality indicators in particular that I think may help distinguish them more.

Anyways, here goes.

Quality++ Thoughts:

To preface, this is my go-to quality mod set and is by far the best one out there in execution, I feel. My only real criticisms here are that I do think the mods stray a big close to "big-number-syndrome", where things become more or less impossible to get to compensate for them being extremely powerful.

-The order of magnitude based scaling for probability by default is extremely dramatic, and isn't really meant to scale to having four additional qualities-

Things like epic and legendary quality are made possible to get by higher tier modules and module slots, but there's no way after to possibly make up for the genuinely insane odds thereafter. For reference, an artifactual item from quality++ being four orders of magnitude rarer than a legendary means that the odds of getting a legendary from scratch are the same as getting an artifactual from all legendary inputs. Without some seriously crazy mods alongside things, I think that 1 out of 100 million is just too overwhelmingly unlikely to ever try to pursue.

-Quality effects are a touch too strong-

One of my favorite things about quality is how much of a power boost it offers, but legendary items are already genuinely exceptional. I love the idea of scaling past that and massively extending the late-game, but at the same time I feel that they scale a bit too much. Four times a legendary bonus more or less trivializes everything in the game.

-Quality progression-

While I think unlocking every other quality alongside legendary makes sense, it couldn't hurt to have separate researches beyond that using promethium science packs, or if you're able and willing, even integration with other planet mods. I think this could set this apart from most other quality mods even more and help it maintain a very natural and methodical progression in comparison to them.

Quality++ Suggestions:

-Probability Rework-

Either change the probability of post-legendary qualities to be 4-6 times less likely than the last, or make the entire probability scale follow factors of 7-8 and not 10. If you're looking for references here, many of the mythical quality mods out there add options to do this in the config.

The idea behind the math is below, comparing vanilla probabilities vs quality++ probabilities of getting to a maximum tier item.

Current: One in 10,000 vs One in 100,000,000 (10,000 times harder)
Custom Quality Scaling Change (Factors of 10 up to legendary, then factors of 4): One in 10,000 vs One in 2,560,000 (265 times harder). Vanilla quality chance untouched.
All Quality Scaling Change (Factors of 6): One in 10,000 vs One in 1,680,000 (168 times harder), legendary and epic are ~8 times easier to get.

-Strength-

Changing vanilla scaling and integrating into mod, to make custom qualities more powerful by comparison: 1.5 levels per quality tier, up to maximum of 12.
Keeping vanilla scaling: 2 levels per tier after legendary, up to a maximum of 13.

Another possibility would be to dial these back slightly and make the artifacted tier three or four levels higher than the previous one, to really set it apart. Maybe scaling one level per tier past legendary up to something like 8, and then jumping to 12 for the final tier. I really wouldn't recommend going above 10-12 for the maximum bonus if they're not going to be configurable.

-Design-
Possibly change "artifacted" to something else, like "Ultimate", "Unreal", "Ascendant", or "Superior"? "Artifact" almost makes the object sound a bit outdated. Also may consider shifting the colors around a bit, possibly even alongside the vanilla ones as the current tiers don't really follow an easy to read color scheme.

Shiny Qualities:

This is honestly why I'm writing this up. Amazing idea for the quality system, and the only of it's kind that I've seen. However in its current state I can't see it getting much use, unfortunately.

-Probabilities are far too low-

1/2000 on top of the already extremely low probabilities makes anything here more or less impossible to get. For the maximum tier, this rarity on top of that puts it fractions of a trillion for probability. Especially given that some of the buffs are for things like electrical poles, I don't see a scenario in which the current probabilities would ever allow for them to be used in any reasonable amount.

At minimum, I would drop this probability to 1/100. I would also allow for accumulating shiny-tier materials and crafting with them - this still requires RNG and "fishing" for shinies, but I feel that without it this would be nearly impossible to automate at scale. It also means that if a recycler or intermediate plant produces a shiny it won't be completely useless.

If it's possible, I may also consider more complicated mechanics. The 1/2000 chance would make sense if there was a way to increase it - perhaps shiny chance goes up exponentially with higher quality bonuses, or there's even a dedicated module to boost shiny chance specifically? I think that possibly even making it an alternative route to normal quality scaling could be extremely interesting mechanically.

-Lack of a 9th tier shiny-

I really love the idea of these as "in-betweens", but I also think that there should probably be a shiny to match tier 9, possibly even just a straight up tier 10 one if going all in with this. It feels a little strange to not have an ultimate variant of the highest tier quality.

-Shiny scaling-

While the idea of the previous level + 2 is a great idea for power, I think that it also makes things confusing and makes shiny rarities for higher tier items proportionally less effective. I'd consider making it a +25% - with a maximum level for the base mod of maybe 10, for an absolute cap of level 12.5. This is still insanely powerful but I think helps dial things back overall and ensures that both higher and lower tiers benefit, but do not outshine those above them outside of their specific niche.

-Shiny effects-

I think shinies need more varied effects, and for their specific effects to be a little bit less insane. What I would suggest is that at each tier, shinies affect one major stat, possibly two at higher tiers, for a few different specializations. Only affecting one stat on one building is I think much too niche.

For instance, a rare shiny could specialize in electrical networks and boost wire reach for electrical poles, maximum accumulator charge. A legendary could specialize in manufacturing and increase module slots for assemblers, productivity in chemical plants, and mining speed for drills. Mythic shinies could do weird things like give weapons damage bonuses (there are mods that make quality do this that might be nice references), increase science pack productivity massively, and so on. The top tier could even give a sizeable extra bonus to everything but specialize in personal equipment, making it a jack-of-all trades but not necessarily the best for every single situation outside of player gear.

In general, I would favor additive multiplicative bonuses over flat ones. This especially applies to the current one for the equipment grid - a 30 by 30 equipment grid boost is almost arbitrarily large, and I think at most it should be a +25-33% increase when considering that the base tier also increases size. With current math, an artifactual mech armor would push north of 60 by 60, and I don't think there's a way to even use, let alone balance, having 3,600 equipment grid slots when the base game is built around an absolute maximum of around 300.

At the absolute most, I would have these be +50% to +100%. Giant bonuses like +250%, especially those that end up stacking multiplicatively, could end up completely trivializing a lot of game mechanics just from simple luck. Like all things factorio, the end goal of shinies I think should still be to get them en masse, so they should be balanced around that possibility - both in terms of being able to get them, and not breaking the game, in large amounts.

-Design-

I think perhaps shinies should have brighter colors and slightly different icons to differentiate them from their base tiers. The legendary shiny could be yellow or light orange, and possibly have a different icon. I mainly say this as things like the rare shiny just look like a recolor of rare, which I don't think captures things.

-Conclusion-

I love these two mods. I would say that the core of my balancing feedback is that the higher levels are nearly impossible to get, but if acquired, end up being game-breakingly strong. In a game about automation and mass production, I think that toning both of these down to strike a balance would be ideal.

I also do think that it wouldn't hurt to lock certain higher tiers and shinies behind specific research projects. Unlocking legendary on Aquilo and suddenly having to account for four more qualities above it immediately would be a bit overwhelming, and I think shifts a lot of what's best left to late-game progress much closer to the midgame than is ideal, especially with mods.