I like this idea.
The option to choose either a Support or Defense ability on each of the 9 tiers of the Support or Defense powersets would make full use of the Multiple Builds system, especially now that Incarnates have access to 3 different builds.
In my personal play style, there are always one or two abilities on my Support powerset that I never use. For example, on my Cold Domination Corruptor, I would love the option of taking a Defense-oriented ability (ESPECIALLY a mez protection power) instead of Infrigidate or Snow Storm. I never use those abilities because they are both replaced by Sleet.