I can't help but think that Mike Mangini would be a great fit. He's extremely technical and could easily wrap his head around any time, tempo, style change that DT could throw at him. He's a full time teacher at Berklee school of music (Where MP, JP, and JM went to school for a year or so) and has shown that he can step away from that to pursue tours in the past.
On his FB page recently he's said that he's been practicing a ton (no surprise there, but given this topic I figured it may have some correlation) and I know that he's married with at least 1 kid- so yeah, family guy (no, not the show). Also, at a show in Boston- don't quote me but I think it was early 2002- he performed on stage with Dream Theater when MP pulled him out of the crowd to join him on the original Siamese Monster.
Also someone that has shared the Siamese/Albino/Mirage/ and whatever other two-headed monsters MP has come up with recently is Jason Bittner. JB was brought up earlier in the thread and I completely agree that he's a cool guy and certainly family oriented (also from NY like JM and JP). I just can't see JB walking away from Shadows Fall to pursue DT. I know a lot of his music and can't say that I've seen anything on the technical equivalent of DT. With that said, I can't judge him without seeing what he can do.
Charlie Benante is someone I just don't see melding well with DT just from a stylistic point of view. Charlie's playing has always been somewhat straight up and down without a whole lot of frills and I can't picture that with DT-- as odd as it sounds, I think his playing may be too simplistic.
Ah well, DT Nation will just have to sit around patiently (or not so patiently) waiting for the announcement-- then a whole new buzz, investigation, bashing, praising, etc. phase will commence when there is an announcement. I'm eagerly waiting with the rest of you.
AJ