An amazing feature would be the option to change grenade types from clusters to normal- sometimes you need to throw a grenade at an airborn target, without raining down explosives on yourself. They are also a major pisser offer in freindly fire enabled team matches.
Edit: sorry, I didn't make that very clear, I mean like a button to switch grenade types in-game (tab anyone? I know its already used but surely having it next to switch weapons would be the most logical) so when you pick up cluster, you can change back to frags, and save clusters for when you need them.