Why do you think combo abilities (abilities that added different types of attacks to combos) were removed from the series after KH2? 

For some games *coughdayscough* it was probably more difficult to implement them. DDD and BBS seem like they could easily implement them (especially BBS) so I guess either

1. They've been cut from the series

2. They're going to bring them back for KH3.

They need to bring them back, and also add the C-C-C-Combo Breaker from Killer Instinct 

Nomura likes to test new stuff in not numbered title games, to come up with new systems, new types of gameplay, but he sure doesn't like to change much well it's about the basic KH model. He could have given up on them, but I'm confident we'll see them back in KHIII

Because yolo.