f(x,y,z)has nothing to do with IDEs, either extant or idealized. In the SIP meeting, Adriaan took the stance that it's an editor issue. I would say that comment folding is an editor issue; or #ifdef as an editor action to pull source from two git branches is an editor issue. Here, the equivalence of two syntactic forms has nothing to do with tooling; all syntax is trivially just some tooling paraphernalia. Unless the trailing comma form is demonstrably ambiguous in a way that harms error reporting, then it's no different from the presence or absence of semicolons.