We used to spam battle regimens, it's not too bad once you get a group used to it. We'd have one person as the "opener", usually a MRD since he could keep autoattacking while it is open, then all the melee would throw in theirs (no particular order), then the mages would throw in theirs and close the regimen.

It seems complicated, but it was well worth doing and only takes a few seconds if you are on the ball.

I'm actually thinking that the new combo system would make that old battle regimen system a bit difficult though. I really hope they find a decent system to make this work. (even if it is not battle regimen)

Having players do cooperative combos might be cool, though.