As we said on Indiegogo, we had plans to add a Car and a Vertical Lift (or some kind of Vertical Vehicle).
http://www.indiegogo.com/projects/blackvoxel--4For others vehicles, nothing is fixed but we think about some fun gameplay ideas like a rocket, a parachute, skis, some other kinds of aircraft. The idea is vehicles that would be fun to pilot. In fact, development time is the only limiting factor.
But the more interesting thing we have to speak about is here : we are working on a volumetric displacement system that we will use for doing volumetric vehicles that could be voxel-train, or a voxel-airship. Because these kinds of vehicle have no interest in moving only the player like the aircraft do(and the car will also do).
But with the new programmable robot functions, you'll can do yourself some kinds of moving voxel vehicles (even if it will miss some functions).
Further, we'll add some powerfull functions to the Squirell api to complete this : mass voxel moving(3D bloc voxel transfert) and some player physic interaction.