I think it'd be neat to get a buff class like Arcanist supposedly was that had a mini-game involved with buffing. We already have little game things associated with DoH, it would be great if they transferred into combat too.
Bard could apply this, for example a small set of strings could appear on the screen and you simply have to hit the right one at the right time over the course of the casting (would have to be fairly slow-paced) purely to make things more interesting.
I loved bard back in Aht Urghan merit parties for the fast pace and the fact you essentically decided if the party did well, but something like a mini-game would be great for making those tasks more fun.

I think this could be applied to all classes though to be honest, special moves that acted like the limit breaks of old where you time button presses to get more strikes. It would have to be client-side to avoid lag, but i dont think that would be too big a problem although I wonder how exploitable it would be.