Any boarding action or Imperial Assault game would take waaaay longer than an actual X-wing dogfight. There's no way they would take place at the same time. Maybe an Armada scale fight, that I could see.
That is a concern, I've never actually played Imperial assault so I'm not opposed to cherry picking it's hardware and using what I think works and ignoring elements that get in the way. Or maybe the timing could work if you put a 2:1 or 3:1 ratio of turns per round. But "no way" to make it happen? Never tell me the odds ( especially if you think they're 0)
I would think that the boarding should happen once the main X-wing battle is over. Or....you board, but you don't know how the situation is going on outside. Maybe you capture the ship, but your side has buggered off?