The metagame would be more interesting with Dream World. I don't see why we can't have it. The only arguments against it (afaik) would be either: 1) without DW the metagame would be ~official~, or 2) the occasional release of a DW release keeps the metagame fresh. This metagame is being done "for fun," so it doesn't really need to be playable on the games legitimately anyway. And I think we should avoid complex bans unless we really need them. Every Pokémon that has either Sand Veil or Snow Cloak has a second ability thanks to DW, so a Sand Veil / Snow Cloak ban can be done. Also, Dream World includes unreleased items like the stat boosting berries and Soul Dew, right?
By the way, the following tournament themes will be for CN: BW NU, DPP OU, Adv OU, and GSC OU. Basically, it's all of the past generation OU tiers sans RBY, with BW NU. Once CN is over with, mostly everyone will have experienced those tiers and we could a voting poll afterwards.