Basically, my suggestion is this (if it's possible):
With each set, either on certain or all tiers, have a choice between two powers (maybe more if you really want) for the player to take. Thing is, they can only take 1 of those. This allows for greater set customization while staying within balance, and can help with variable builds for teams or soloing, whichever you really like to do, which is something certain AT's really need. The following are some examples.
Melee Support: Their support set being a combo of personal defenses every few levels, a couple auras, and mostly PBAoEs. Inherent would make their support powers more effective the more allies they have in close proximity, but still decent when alone.
Variable solo and team build: With the Defense and Support powersets, each coming with two power choices at each tier. For example, in Cold Dom, you choose either Infrigidate or a personal Ice Shield. In Regeneration, you choose either Fast Healing or something similar to Soothing Aura.
This way someone may choose to build a purely solo build on their Defender, Corruptor or Mastermind, or a mix, or purely team build. On a Melee character, it would give them the option of a purely team support build, or a mix, or solo.
So, if you think this might be a good idea, or have some suggestions on how to make it better, let me know, or let a Dev know if you like it.
-Heitomos
Isn't this what a second build is for, which is something we already have?