going to be waiting a very long time, then. 5.2 isn't on
LuaJIT's roadmap at all.
But you can compile LuaJIT to have a
lot of Lua 5.2 compatibility, although without _ENV and
overriding __gc for tables. I don't think Mike P regards the
latter as intrinsically bad, but he will wait for his new
garbage collector in 2.1 before implementing it.
Someone posted an _ENV patch for LuaJIT a while back: