Blizzard isn't Valve, they will (and have in the past) make balance changes to discourage this stuff. Class limits were only a necessity in TF2 due to Valve's ineptitude and I think people should give Blizzard some time to showcase their dedication to the game, even if it means sometimes being stuck in kind of lame metas for a bit, but that happens in every other big competitive video game too now and then.

Not that it matters because in a month or two they'll drop their official ruleset and everyone will use that no matter what, but still...and there's no chance they will class limit 1 because that would a) be against everything they've said about this game and b) just re-spark one of the myriad of issues which in the long term hurt competitive TF2's success - the big rule changes from the pub game.