[snip]
"Given Metalua is written IN Lua (to my knowledge) - should it be used by
LuaJIT-2, will it use the new byte-codes automatically or does it have them
defined as constants that would need to be changed/altered?"
The answer is no: even if Lua JIT had bytecode frontend, metalua would
not be able to adapt itself automatically. Metalua inherited it's
backend from Yueliang which is just rewrite of several modules
(lcode.c, ldump.c) from C into pure Lua. When this modules change in
original Lua sources, metalua backend must be changed to accommodate
it.