I would like to have all vehicles of the halo universe in Halo 4!!!
Which vehicles are going to be used in the campaign depends on how the story of the campaign is going to be.
But yeah, a scarab playlist would be cool, something like invasion in Halo Reach, for example where one team has to get from A to B and the other team has to defend and destroy the scarab. Something like that would be cool!
And of course epic space battles with spaceships of the humanity and the covenant with different gametypes/playlists might be pretty cool! But in the forge, there actually have to be all vehicles of the halo universe!!
343 shall make us just very happy concerning the vehicles, that are going to be used in Halo 4!!!