Already an amazing character in his current state.
The hustle timestop off slider is a chef's kiss

Though, a tandem summon flip would be amazing.

A huge thought, is having Jotaro enter Timestop if his opponent has already cast it. IF not Dio's then against himself in a mirror match.

Maybe some expensive form of Timestop where it's unblockable? Or have it be a free cancel-able move, costing a bar instead of burst.

Regardless of the direction he's headed in, the vision of this hardcore stand user is clearly badass.