In other words, in your 2x3 grid of syntactic x expressiveness, I want the two points corresponding to classic syntax x {existential quantification, GADTs} to be removed from the language. My second semi-proposal also makes each of the three points corresponding to the new cool syntax a separate extension.
I see, but why are you opposed to have the classic syntax still support existentials (though foralls) and GADTs (through equality constraints). I would make sense to me to keep this support around.
I am opposed since a) it requires the addition of extra syntax to the language, and b) we have another, better, way to do it. Somewhat pointed, I don't think the C++ way of putting all imaginable ways to do the same thing into the language is a sound design principle. If we have two ways to do the same thing, and one of them is considered prefered, then I see no reason at all to keep the other around. What I'm arguing here is that the GADT style syntax is truly preferable, and thus the other should be removed. Cheers, /Niklas