IIRC they said it was a new universe, so not starcraft, warcraft, or diablo. Unfortunately this probably also means no rock and roll racing mmo...

If multiboxing is allowed then it definitely should be considered in the game design. Do it in a way that makes it possible in non-annoying ways(/follow, /assist), while making sure boxers don't have a huge edge over players that don't box. This isn't something that a huge amount of time should be spent on, and the game should be designed around the solo player first and foremost.