The meta of Dominion will be Teemo, Heimer, etc.
People who make stationary defensive objects will be invaluable. Likewise, the semi-global ultimates of champions like Pantheon and Twisted Fate will be incredibly valuable. Shen is probably going to be the tank of choice.
Mobility is going to be key, you're right. However, being able to defend globally is going to be really powerful as well.
Survivability will be no more or less important than it is on Summoner's Rift. In fact, we may see an increase of skirmishes, so squishier champions will be able to face-off without tanks around.
I'm excited to see Heimerdinger become useful for something other than making wards invincible. I don't play him, but it'll be neat.