Resolution itself has absolutely no affect on storage.
Resolution doesn't have an effect on storage, but 4K textures do, and heavily so. You know they'll be doing 4K textures if they push 4k, so, there.
720p point is exactly what I'm trying to say. By keeping 1080p as the cap on a more powerful system, it is likely that an increasingly vast majority of the games do run at 1080p while boasting better graphics than they would if they had to render at 4K with 4K textures.
Yeah, that's exactly what they've done with the Wii and then the Wii U (backwards compatibility, including controllers and a few new features).
Eh... the Wii U was nothing like the Wii, not at all. It had the software/hardware backwards compatibility but was overall a much different product. Had a weird new controller no one understood, an incredibly slow OS that was far worse than the Wii's, and was honestly garbage at doing what the Wii did best - local multiplayer.