It would be quite pointless actually.
These days I can hardly find 6 active servers in ROOST, and half of them are tank servers, the other half are full most of the time, so I can't join.
Once ROHOS is out, those few servers will probably disappear.
Other than that, when you can join a game it's still very enjoyable, I'm really glad I heard about this game on the Bad company 2 forum the very same day it was discounted on steam, I found the game I've always wanted to play.
well I think the idea is to breathe a bit of life back into ROOST with new players, even if its for a few months.
But the way I see it, most of the preorders are going to people who already have ROOST (I guess they can gift it - which also wouldn't be a bad idea to get the word out).