Both sound incredibly useful, thanks! I gave +1
I was having a look at the list of old TPT versions. Why are all the dates all May 20th? I don't see an easy way to fix that, even if you get the real dates off a master changelog or the metadata it would take time, there are alot of updates. It does seem to have affected the order though, and in a weird way too. It's not in alphanumeric or alphabetical order like you would expect, the files are all out of order. That would make things tricky as all hell if you were trying to determine what version any given feature was broken or removed, like I was about to do.
I know what my most wanted feature is, I have wanted it for a long time, and it becomes more and more necessary as tech evolves. Multithreading!
If you're looking for subframe-friendly functionality like easy layering, you might want to check out my mod (https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=21251). Anyway, multithreading would completely wreck subframe, so I'm not sure that's something you really want.
TPT already uses threading to a small extent. Threading the particle simulation is near impossible, and the workarounds required would likely ruin most/all of the gains from threading it. tbh i dont know if it's possible at all.
An entirely diffrent game should try and do threading. TPT itself can't do it, and threading would break even basic electronics (Like, say, SPRK itself)
TPT has had that for ages. Lua scripts can make new elements.