If the goal is to simplify accessing Perl internals for module authors, creating a wrapper macro/class ( XSS = XS-Simple ? ) for a new API seems the way to go. Preferably in a modular/ linkable way. Since this would rely on standardized XS it should also be backwards compatible.

Changing the XS implementation is another beast, while this might benefit core devs I doubt there is a mid-term return of investment justifying the risk.

Again, theoretical thoughts. If I'm wrong about the details, please enlighten me. :)