Hey there,

you are doing something that people asked me for but I never did it because of motivation. But the base concept already exists in my mod:
https://mods.factorio.com/mod/hot-metals

Maybe you want to make your mod an addition to my mod (as in, you require mine and add additional concepts)? That way you would profit from the already existing user base and we could promote each other. Browse the open discussions over there for ideas that came up.

That's just an idea. "No" with any or no reason is a totally fine answer.

Thank you for the offer! For now I want to figure out what is (or isn't) fun about the way I've implemented things. Once I understand the answer to that question I shall give it more thought! I notice you have a much bigger focus on waiting for things to cool down whilst mine focuses more on keeping things hot, only occasionally wanting to wait.

Would you have any objection if I toyed with ideas like making a few metal products need that coolable state?

Feel free. Using the hot state for more than waiting is what I thought is the addition of your mod.

Another idea I had, was using the Convector from Hurricane to re-heat metals after they cooled down (it's at the very end).

I'd agree that's the focus! I wanted to break up the usual massive resource production to encourage keeping high throughput.

Also that list of buildings is utterly beautiful. I'm bookmarking that. The Convector being a better re-heating building sounds lovely. Currently it supports regular smelters for it. A better one would be fun!

Furnace is problematic because it would smelt iron into steel instead of heating it up. Feel free to contact me on Discord ("cacklingfiend." or join my server https://discord.gg/ufvFUJtVwk).

The furnace works by requiring heated iron to make steel. Whilst cold iron gets turned into hot iron. It makes the builds more complex, but that's the point.
This mod does a lot to modify existing recipes to require heated variants as ingredients.