That sounds like a reasonable proposal that we could at least consider. But I think it will not fly. Presumably it doesn't apply to tuple displays, because of reasonable examples like ((a := f(), a+1), a+2), and because it would create an ugly discontinuity between (a := f()) and (a := f(),). But then switching between [a := f(), a] and (a := f(), a) would create a discontinuity.

For comprehensions and generator expressions there is no such discontinuity in the new proposal, since these *already* introduce their own scope.