Agree with Raymond. If the goal is to pass something else, then functions that want to make use of that "something else" have to be modified anyway, in which case also changing the call type wouldn't hurt (assuming the new value still fits into the flag options, but it should).

Only drawback is that adding a new calling convention breaks *calling* code that does not go through the C-API for calling functions, or that otherwise makes direct use of the calling convention flags. But that should be very rare and I think it's acceptable to require such code to be adapted. It would very likely be amongst the beneficiaries of the proposed calling changes anyway.