Exiles Morph is the best developed and most interesting, but I'd be interested to see original Changeling come back. We know very little about him - what even led him to Factor Three when AU versions of the character all tend to be more heroic? (I mean, I know why, it's because he was completely reinvented to become cartoon Morph, and then cartoon Morph influenced the later AU versions.) But I'm curious about Changeling's history. It would be funny if he just blew off his past misdeeds like Emma in Morrison's run - "Oh, I was very confused and probably on a lot of drugs." And writers could gradually develop him more in the direction of animated Morph. I could imagine revived Changeling having a more serious personality, but with a dry, sarcastic sense of humor, and gradually loosening up and becoming friendlier as he figures out what to do with his new life. And apparently AoA Morph also started off as Changeling with a "morose" personality, so there's precedent for that kind of change.
And honestly, Ben Deeds and Changeling/Morph can easily co-exist. I think Deeds' power is a bit different - his body emits chemicals that make people like and trust him, and his shape-shifting seems to be a complement to that, taking on similar features to whoever he is talking to. I think there's an AU version of Ben who takes the codename Amity instead of Morph, he could switch to that.