But MLS would definitely try to spin it around saying hey, this is the newest MLS team having success already.
So theoretically speaking, if the Impact were allowed entry into MLS in 2009, and they kept their current team intact, how good of a team would they be? Personally, I'm surprised how well the impact have been playing against MLS teams. Gives me hope than when Montreal gets a franchise, the current team won't need to rebuild from the ground up and they'll be a competitive team from the first season.
Right now they would probably be consistently fighting for a playoff spot. As others have stated before, USL rosters do not have as much of a dropoff from their starters to the bottom guys. The Impact would be able to hold a steady form better than most MLS teams who have dropoffs when players like Donovan, Blanco, Beckerman, Angel, Emilio, etc. are out. BUT, they still wouldn't have enough talent to consistently take out some of the better teams in the league, especially if they made if to the playoffs.