Durable champs with anti-attrition built in. These are the ones that may end up being considered OP.
It was mentioned that the addition of health shrines was designed to specifially counter their large advantage. It is likely this won't be sufficient. Especially since the durable champ can use it too.
So a list of such champs might look like, from MORE likely to only POSSIBLY:
Blitzcrank (i'm biased, but I really think so)
I can't comment about stealth champs or healer supports, but i'm sure they'll have some kind of useful niche. Karma might become popular on this new map because her kit seems built for it (Harrass, sheilds, aoe heals, speed buff/debuff).
Heimer will obviously have a strong role as well.
I want to put some emphasis on how terribly OP Mundo is gonna be. While mundo is widely considered to be crappy at reasonable levels of play on SR, he is an absolute beast on TT because he is great in small fights and skirmishes. Cleaver is a low CD, Decent damage, long-range poke. His ultimate gives him bonus speed and puts him back in the game, it is also on a fairly low CD.
If you've played 3v3s you know what Mundo is gonna look like in Dominion.