Actually, this is what I was hoping for in DLC...something with some classic cold war weaponry!
If they give me a Type-56 or AKM or AK47 in 7.62x39...then I'll be all over this (especially if the classic weapons can be used across the board). It'd be less accurate but do a damned good bit of damage at close range but it'd have a lot of drop.
Hell, you could give the assault an AKM (or AK47 milled), the Medic could get an RPK, the engineer could get an underfolder (maybe a Type-56 as there were a lot of them in 'nam), and the Recon could get an SVD (dragonov) or an SVT-40 or perhaps a Mosin. They could also work in an SKS in there (perhaps as an across the board unlockable).
On the US side you could have classic M16s (less accurate than a modern M16, and in full auto instead of 3 round burst and with slightly more damage (less stable bullets than the current issue rounds as I remember along with a different twist)). You could have classic wood stocked M14s, M1 carbines, silenced Mac-10s and Car15s, British issue FALs, and just a shit load of stuff.
If they give the ability to use these weapons on standard maps as well (and they wouldn't be unbalanced so much as different) that would be great. I already love the hell out of BC2 (my favorite multiplayer game of the last two years)...and this seems like the direction I'd like to see them go in with the expansion. Its a hell of a lot better than a spattering of overpriced fucking maps from the previous game (that happened to be a much better game....COD4 > MW2 IMHO).