I take this rumor with a grain of salt. For these vehicles to do any serious motion on a motion base, they would have to be locked in to place, like Gringott's already is, as it's on a track. All Gringott's has to do is raise some bars, or put a lock into the wheels. For a trackless vehicle to be stabilized so that it can do any serious, it would need to be braked AND held on to the motion base in some fashion. Now, they could ride in to a 3 sided blocking device, and the back side raises up in to position. But that would require perfectly precise movement, and I would think you would still need to lock the RV to the floor in some manner. I don't know what the tolerance is on Disney's vehicles positioning, but it would need to be very low. And the locking very quick. Gringott's does this, but then the motion is far from Spider-man level.
Perhaps this will happen in a finale scene, but the RVs would likely have to leave for their own separate bases, sorta like Ratatouille does near the end.