Rock Band 3 is one of my favorite games, however it isn't that technically impressive.
I was thinking of a 4th Rock Band for the 4th Playstation. giving Harmonix the chance to put in technology that will enhance the experience. they could improve the possibilities, the graphics, the mechanics and include a system that checks what you are good at and helps you choose songs that have those same elements. They could easily make RB4 a game you WANT, just as long as they give their fans exactly what they want.
If they made RB4 I would buy it, just make sure my PS3 GH controllers and RB3 DLC works with PS4
if they take it slow and be careful and don't release 20 games at the same time it could even be profitable.
(I mean Guitar Hero is out of the picture, right? and it can't be possible that EVERYONE hates GH/RB now. and if you do, thanks, you really improve my life with your opinion)