If you mean that "t[[x]]" is a function call like "x(t)", then "t[[getmetatable]]" would replace "getmetatable (t)" only, it may still return nil if t has no metatable
So t[[getmetatate]].x could throw an error (indexing a key "x" in a nil object which cannot be indexed)
And so is radically different from "t[!]" that I proposed (using "!" as a new keyword along with "!keyword" or "keyword!" for other language extensions), because it is two functions calls, one for "getmetatable(t)" and conditionally replace it with a new table with "setmetatable(t, {})" if it's nil, then a conditional "__newindex(t, k)" or "__setindex(t, k)" or "__getindex(t)" for getting or setting any further key with "t[!][k]"
What I proposed also allows "t[!][!]" for metatables of metatables with the same implicit metafunction calls (getmetatable, setmetatable, _newindex, __setindex, _getindex).
get/setmetatable() and fgetenv/fsetenv are not properly integrated in the Lua language which uses some "magic" (with dependance on a "standard" library loaded in the environment) and no clear semantics.
