i had a similar thought myself. Sentinels are an interesting development. if only because they show what is possible just by mixing and matching established sets. here's some ideas i had. of all power sets, 3 stand out as not being shared among other AT's: Mastermind Pets, Blaster Manipulation and Dominator Assaults. Masterminds can keep the pets as their signature.
The Catalyst: (aka The Fool, Enabler) concept being Jackie Chan, MrBean, JarJar Binks etc. that hapless individual that is just lucky or klutzy enough to make insane things happen.
primary - Assault (Dominator secondary)
Secondary - Buff (Defender Primaries, Controller scale)
The Ace (aka Jack of all trades): concept being that unique member that always seems to have the right tools to be able to pull off the right move at the right time. also blapper?
Primary - Manipulation (blaster secondary)
Secondary - Assault (Dominator secondary's)
inherent power: Competitive streak - each teammate increases power secondary effects by 2-5%, each other Ace on the team drops acc/dam by 2-5%. this would represent the team synergy that builds with an Ace. Also the mis-coordination and interference when you have two people both trying to be the Ace.
The Commander (Aka Bully or action hero):
Primary - Melee (buff secondary effects, tanker scale damage)
Secondary - Control (reduce damage, duration and secondary effects, leave magnitude as is)
what are others ideas and thoughts?