There's less demand for this in Minetest, though, because modding Minetest is already super easy in Lua—you don't have to learn Java like you do for Minecraft. But you can't load a Lua mod even in Minetest if you don't run the server.

Mobile-code environments for mutually distrusting code turn out to be more difficult than people used to think, but now we have multiple off-the-shelf battle-tested implementations of JS for that. And you can coerce Lua to do it, kind of.