I am utterly charmed by Lignumis and am close to finishing out a full run with it enabled. I've got all the planetary sciences going and am going back to build up Nauvis a little with all the new toys before looking at Prometheum science and ending the run.

Here is something I noticed: the new plastic recipe has an interaction with lubricant. Normally you produce so much plastic for chips that you can produce lubricant as a minor byproduct and never have a problem. For my Lignumus run, I went all out on the organic plastic recipe, so I'm using very little light oil and petroleum. I just use it for launching rockets and for lumber mill fuel :) . As such, it's hard to make lubricant due to light oil hitting a cap and the refineries shutting down.

The workaround I am doing is to have a sub-factory that goes advanced oil processing -> heavy oil -> lubricant, and then I void the light oil and petroleum by converting them to solid fuel. This is very wasteful, though.

It would be neat to also have an alternate lubricant source that corresponds to the alternate plastic source. As it stands, I am not sure if it is even the best choice to use the alternate plastic recipe on Nauvis. I did it because I wanted to try all the Lignumus goodies, but it may be better from a min-max point of view to stick to the oil-based recipe on Nauvis.

The alternate source of lubricant could be another kind of bacteria, or it could even just be something that down-converts light oil back to heavy oil.

Looking on the forums, I think the simple oil cracking recipe used to produce heavy oil. In the game as I have it, simple oil cracking just produces petroleum, so that's no good for this problem. There's also coal->heavy conversion, from a Vulkanus recipe, but I am not sure about using coal to get petroleum if it is just for this problem. That's definitely an option, too, it just means finding coal mines to pull from.

Thanks for the positive feedback and sorry for letting you wait for so long. I guess by now you have moved on to the next project.

I think the Lignumis goodies are already quite powerful for being such a simple early game moon. Adding more powerful things would probably be too much. In your case, I'm not sure if using petroleum for solid fuel is that wasteful. You need it anyway for rocket fuel. But I haven't tried it myself. Since it's rather niche, I'd rather point to additional mods or use coal liquefaction as you already pointed oil.

I found these mods:
https://mods.factorio.com/mod/Petrol-Condensation-Reload
https://mods.factorio.com/mod/oil-condensation

Thank you for the thoughts and for sharing your design perspectives.

I am not stuck and do not really need anything. I was just fishing around for ways to massage the setup so that the alternate plastic recipe may be usable while creating an intended level of challenge and style of solution. I hadn't fully considered the power increase that any new recipe would unlock.

Those two mods for reverse cracking seem like what I will try in the future, unless there is another idea that comes up. I like how those are surgical changes and how they are pre-existing mods.

To be clear, I ended up not using the solid fuel, because I already had the chain to rocket fuel that you are picturing. For some reason in my save, there just aren't enough rocket launches. When I've read forums about how people deal with petroleum maxing out, the usual answer is to increase science production as a whole so that it drains petrol->plastic->chips. That answer stops working if you are using an alternate source of plastic.

I am curious why others do not run into this issue. Do you have a guess why? I take it it doesn't happen in your own test playthroughs.

I can post a save somewhere if it would be of interest. I'm not sure the best way to do that.

Another answer, aside from the mods you link to, would be to set up coal liquification. The wiki even suggests that as a way to make lubricant. I thought about it, and I think I avoided it due to needing calcite and coal as inputs. That seemed a pity for something that was previously a pure fluid-based recipe, so I worked out the voiding-based solution.

I really like the new plastic recipe, and it's very powerful. It feels like Gleba but a little simpler due to the alternate recipe for handling spoiled bacteria. It still took me a few tries to keep it from jamming up, but I think got an arrangement in the end that works. (True to Gleba, I seem to never be 100% sure there's not another jam condition that I overlooked!)

"I am curious why others do not run into this issue. Do you have a guess why? I take it it doesn't happen in your own test playthroughs."
I never used the recipe outside of Lignumis. I didn't even think it would be practical until I saw people using it. I think people usually don't switch completely but rather use a mix of both recipes to reduce the load on oil. In your case, I think adding a mod to get more balancing options for the fluids is a very valid option.

"I can post a save somewhere if it would be of interest."
I think that isn't necessary.