In regards to those made Tranquil, I'm very scared of those who had legitimate reasons to be made Tranquil. They will have their powers back, and will no doubt be overly emotional and angry at what was done to them.
Ah, good times.
This is why I think it would be so interesting. The tables would be turned on *everyone*. The hunters become the hunted.
As for Cullen, sure, there are Big Important Things he would do to safeguard the world... but I'm more interested in what his very personal response would be about himself. Given his approach to the Circle, he seems to be a Greater Good kind of a guy, so I always imagine he'd have a hard time learning to take care of an individual's needs, including his own. Particularly when that individual's needs are not strictly aligned with the Greater Good.
I'd love to see that in his romance, actually, as of course I've said many times before.