So one of the staff members at origins told me that focusing solely on killing the enemy mage has a very low chance of winning compared to trying to achieve domination victory. He estimated that killing the mage tends to work around 35% of the time, and domination victory 65% of the time. And it's even worse on larger boards. From what I've seen, going for domination victory tends to be a late-game strategy in the format, while killing the enemy Mage is an early strategy. How might this affect the health and diversity of the domination metagame?
I would actually say the opposite. I think that in a domination game, you should go for the v'tar first and shift to trying to kill the opposing mage as a back-up plan if you're losing the V'tar race.
The V'tar orbs are incrementally beneficial, since you gain 2 mana/heal 2 damage when you activates them, and then 1 for each V'tar you gain during the upkeep. On the other hand, killing the enemy mage is all or nothing. If you deal all but 1 damage to the enemy mage, you still haven't gained a concrete benefit from doing so. Worse, that work can be undone by healing. There doesn't seem to be any way to make the other player lose v'tar they'be gained, though.
Winning by killing an enemy mage is still possible, but it's difficult, because the pace of domination is so much faster than the core game alone. My deck that I played against Aaron yesterday was designed to make sure I could reliably get a v'tar orb and galaxxus out by turn 3, and it's actually possible to even get an orb by turn 2 (although I abandoned those lists because I wanted a little more staying power.) If domination becomes a standard tournament format, I think the metagame is going to evolve around taking those turn 2 and 3 orbs.
The real elephant in the room, though, is Galaxxus. That card is so good in the format that I can't see competitive teams NOT including it. If you have it as a prepared spell on the turn you take your first orb, you're doubling the amount of v'tar you would otherwise receive, and you're getting mana/health back from it, too. And since it can't switch control in the same way as the orbs, there's practically no risk involved, either. Much like dispel, dissolve, and teleport, it's going to be a staple card for the format that's practically an auto-include.