Been enjoying this mod the last couple days as I plink away at Vulcanus and the challenges of a x10 science run. I noticed the hidden stone to lava recipe in the factoriopedia and remembered seeing it disabled by default in the settings due to the issues of creating lava - it could be used to create iron and copper from stone, basically. I've also been using another mod:
https://mods.factorio.com/mod/bricked-foundry

Surprisingly, there's no direct overlap, so they complement each other well. One thing it does that would make sense for this mod to also do though, would be the separate "molten stone" recipe. In that mod it works exactly like melting iron/copper ore, but for stone, so foundries can be used on Nauvis etc for stone products, just like iron/copper, while avoiding the issues of lava.

I figured it would make some sense doing something similar here: lava+calcite -> molten stone, and then using the molten stone for all the recipes instead of raw lava.

I'm glad you like it. Molten stone is something what I think is represented by lava itself, this is how I've treated it for this mod. That's basically why I won't add "molten stone". But I could imagine looking for some compatibility things if needed.

Do you think that loop or rather iron and copper from stone is broken? If so, I'd need to rebalance it, as currently I just half the resulting lava.
Also, do you use the bit more complex option with extra calcite cost?

Currently I'm working on some other small mod for casting some science, that could something for you as well. Now that I know that somebody is waiting for it, I've got a reason more to finish it sooner than later.

Haven't played with the option on due to the balance concerns. And, yeah, lava is molten stone irl, it's just the gameplay effects that I figured it'd help avoid.

But it occurred to me that the lava to metal recipes could be disabled outside of Vulcanus to achieve a similar effect! Requiring a minimum pressure just like foundries and big drills should do the trick.

I just love casting stuff in the foundry for some reason, so I'd be happy to see more mods with it :)