That's fast as most full memberships of * take 9 - 12 months to get the incoming carrier up to speed, systems integrated and all that sort of thing, before they become full members. Then again, they're already pretty chummy with UA, so maybe half of that battle is won already. I certainly wouldn't expect them any time this year at least.
Will be interesting to see how it goes and when it comes into effect. MX AC US and UA make a pretty good team in Nth Am.