[gvx]

You could take a look at SELÖVE, a (severely out of date) fork of LÖVE that is intended to make it safe to run arbitrary .love games. (It used to be on bitbucket, but it looks like it's gone? I'm not sure if I have the repo locally :/)

Running arbitrary code was such a problem that I just completely ruled it out for bitser. Instead of serializing functions, you can register safe functions as resources. This doesn't solve the upvalue problem, though.