I really want the Command Decks to come back! BBS deck commands were the best in my opinion. I also found it much easier to battle enemies with the Command Deck. Instead of waiting for the moment to press the Triangle button to just press it anytime. Special honors goes to the Drive Forms. I've never played KH2 so I can't really say anything except that it's kinda cool.

Drive Forms, specifically, Limit Form because if Limit Form comes back, Limits, by extention, come back as well, and I like limits as well.

The Reaction Commands must RETURN!! HAHAHA...sorry....

 

Also Limit Attacks with your party members. Why? Two Words: Eternal. Session.

Limit Breaks and Summons

I really want the Command Decks to come back! BBS deck commands were the best in my opinion. I also found it much easier to battle enemies with the Command Deck. Instead of waiting for the moment to press the Triangle button to just press it anytime. Special honors goes to the Drive Forms. I've never played KH2 so I can't really say anything except that it's kinda cool.

Drive forms (or sort of), Flowmotion and Deck Commands (just hope they will be different from the BbS and DDD ones)

drives . flowmotion & a grid system would be nice

Command styles, in some sort of form, like maybe as Limits rather than just being built up by spells and attacks. Although TBH, i'm perfectly fine with just getting back the Battle Menu that we had in KHI and II after having the Command deck for most of the Spin offs/handheld games.

i would like a more advance version of kingdom hearts 2's gameplay machanics

The drive forms.  No question. 

Riku super sayan mode (dark mode)

Command Styles

Aeroga in Next-Gen graphics!!! It saved me in most of the boss fights BRING IT BACK!!!

Drive Forms.

Drive Form, Flomotion, and a new option that allows you to run away from the boss battles if you're not ready.