Lets do something controversial:
Quick Reaction; Feat: Gain one additional immediate action each turn. You may take this feat multiple times, once per tier.
People complain 4e is slow, and they are right. But why not embrace the slow! It’s a part of the game. Turns do take a long time if your people are not on the ball, but some classes like the swordmage and fighter are dependent on immediate interrupts. Why not give them more! Thoughts?