I think if we're playing on the latest balance patch anyway, there's probably little harm in allowing them at Final Round. I'm a player that will be there.
Characters all around are going to be changing, so lack of MU information is going to be somewhat universal. No one's going to be completely versed on every change to every character and how that effects MUs.
So, unless something gamebroken is discovered before FR, maybe let it rock? Can we wait until March 08 to make the decision (a week after the DLC release) from there, I think we can have a better discussion.
Then it's completely tentative. People thinking of using the DLC know they MAY NOT be able to and can work on another option, and everyone else can play thinking that they MAY have to deal with the DLC.