userdata setmetatable

["Grisha" <grisha@...>]

Hi,

Is there some particular reason, why setmetatable doesn't work on userdata
from Lua? We need it in some cases, like loading userdata from file, and
right now end up with exporting something like setudmetatable(mt). If
there's no particular reason for this restriction, can it be relaxed in
future?

Best Regards,
Grisha