Resolution bumps are possible but probably rare if it happens. If there were X360 games that used variable resolution you might see an increase there but for most games a resolution bump would probably require a actual port or remaster. Framerate increases on the other hand are very likely, as we've already seen examples of games that run better than their 360 versions. This will likely be more pronounced on Scorpio. Some games will still be capped because they were programmed that way and the increase in framerate would likely break animations and other things.
This is guaranteed. The 360 stuff on the One S uses it's slightly more power to make 360 emulation a little bit better.
A higher resolution I wouldn't be so sure on, not because it'd be impossible persay, but because "internal resolution" isn't always 1:1 to the screen. But I would expect 30 or 60fps locked for sure.
Mm. I was thinking along the lines of what Dolphin can do for GameCube and Wii U games, but I neglected to remember that it's approximate scaling. While I realize it won't all be 1:1, surely they could find a way to make a universal solution that can handle cases where it isn't 1:1? Especially since every 360 game is widescreen, anyway.
Unless I'm being a complete idiot. Which is very, very likely.