I can't answer your question as I wasn't involved with the design of the proposal. Maybe you'll find an answer somewhere in the review thread or in the even earlier pitch thread.
But I would be interested in what you're trying to achieve and why you would prefer to have the current limitation lifted for achieving what you're striving for. That might also get people more interested in reconsidering the current limitations. I think it's the very nature of Swift Evolution that these things can be lifted if there's a good reason to do that. But you'd have to explain the good reason first, else there are enough other topics people will focus their energy on.