I've read on the forum from one of the testers that they have a 20Mb down/10Mb up link and everything works fine.What kind of bandwidth are you thinking it'll require? I'm moving in the spring to an area where I'll be lucky to have modest microwave dish internet. And I want this sim so bad!
I think the game works on a tile-based pre-load (it downloads the terrain around you in advance) so theoretically, at least in small and slow aircraft the bandwidth requirements should be really low.
I would be surprised if the continuous downstream was anything more than a couple hundred kb/s. Kind of like Elite in Solo mode. They can't afford to make it too demanding.
Now multiplayer could be a whole another can of worms..