It would be sweet if at the end of the game, when Reach was about to be glassed you would switch over to the covenant side and glass the planet in giant covenant halo wars ships. Also, Locust for the win!
If any Halo Wars vehicle is likely to be put into Halo: Reach, it's definitely the Locust. Bungie themselves even said that they wanted to implement the Locust into Halo 3, but they just didn't have enough time or some crap like that...
The Locusts were first seen as drilling vehicles on Reach, so there's a good chance they'll be in game.
Locusts in Multiplayer would be BAD ASS! IMO It would be like a Gauss cannon except with a charge up time, (anti-vehicle).
Locust! I'd rather this than a Scarab. They look cooler, and they're nimbler and faster than Scarabs. Can be driven like a tank with the swivel turret, and you hold down the Right Trigger for the continuous beam weapon.
Screw all the vehicles There is one thing I want: The trash truck from ODST (costal highway) that would be a splatter fest Anyways I think Reach will have much more focus on vehicles because thats the only thing that makes it significantly different from CoD. Most likely they will use vehicles that are already available, and whose graphics have already been created for another game. The vehicles of Halo Wars also have the advantage of already having been tested for balance in that game.