Color matching is an issue, too. Probably not a big deal if you have a set of identical projectors. But, in a LEM setting, it will end up looking like those old big screens with a bunch of TVs set in a wall with one of the TVs on the fritz.
But regardless, even with mismatched laser colors and galvo positioning, it would still be a cool thing to goof around with and you could create some really huge displays. How cool would it be if someone could create a 360 degree laser projected BattleZone game? You would be able to look around and see tanks coming up behind you. That would be so rad.