I did recently figure out how easy is actually is to decompile the versions of ULTRAKILL before the revamp update, but was halted due to the fact the game uses asset bundles as opposed to normally shipping it in the same package.
Essentially ULTRAKILL runs off of what is called the "bootstrap" that loads these bundles in and lets you play the game. If you decompile the bootstrap and recompile it back to windows, the game will work the same so long as you provide the asset bundles. These asset bundles are NOT cross platform. They are proprietary to platform they are made for. It could be possible to try and do some work to make them cross platform, but that is outside my skill range, especially for things like shaders, which are insanely difficult to try and accurately recreate in a way that can be compiled to other platforms.
So it could be possible to try limbo and lust with an older update without the bootstrap, but that really wouldn't be that interesting as in comparison to the newer (non-revamp) updates.