Yeah, right - like this will happen.
If anything does happen I expect it will be a single market place for all XNA based downloadable titles, which will be playable on all Microsoft platforms (PC, console, phone, tablet...). Given that XNA titles are based on .net and are already cross-platform enabled, it would not really be that much of a leap really. (Many current Xbox Indie & all Xbox Arcade games are already XNA based.)
For disc based titles there is no chance in hell this will happen - even if an audience for this existed it would be a maintenance nightmare and unlikely to bring in any significant cash.
So, yeah, but no.