To be honest, I don't see any reason to play RB4.
No exports I can live with, but no RBN is a deal breaker, I also miss customs heavily but obviously I can't use this as a "pro" towards RB3, but if I'm stuck offline anyways, I may aswell play RB3 with customs.
If it wasn't for the awful stock kits and me having e-kit issues on PS4 (for some reason, my floor tom drops notes on PS4, despite being fine on PS3/360/Wii) and my inability to get decent calibration I'd probably be alot more open to RB4, but eh, my 360 is getting used again now.