If you don’t have interest in learning a new instrument, then don’t learn it. Considering how many kids (and non-coordinated people, like me) like playing, and the no-fail mode, I sincerely doubt that Harmonix goons will be taking away your old controllers.
What’s the difference in pro drums for RB? If you already had a good drum kit (like the Ion), expert drums was pretty much already drumming minus the hi-hat pedal (and there are third party kits to mod this functionality into it). The only thing I can think of them adding is having the note charts differentiate from pads and cymbals (they all show up the same on the note track, and you can hit the green pad for a crash cymbal and still get it right). Did they do that? If so, did they retroactively apply it to old songs? What else?
Pretty much that for the pro drums. All drums/cymbals are charted accurately, so you don’t hit the red pad for hi hat or other obnoxious translations.
I don’t know if they’ve always had DIY drum fills (I come from the land of Band Hero) but there’s that.
All old tracks have retrospective pro drums, but most old tracks don’t have pro guitar or keyboard.