Right...these "vehicles" designed in "secret" are nothing but shells that will be attached to the actual ride vehicles. Remember - these are NOT actual cars on a paved track, but are a lot closer to a powered roller coaster vehicle _under_ the track on rails, with the passenger compartment on an arm above the track. Although the rubber tires to in fact contact the track and wear down (and are replaced somewhat frequently).
The actual design of the vehicle can't change much without a serious track overhaul - hopefully, they are working on improving whatever parts cause all the maintenance issues.
They CAN actually handle some variations in speed without having to redesign the track - the banking does not matter for traction, only for lateral forces, so they can vary somewhat without a lot of discomfort. Remember, the top speed doesn't actually happen until near the end.
However, if they DO vary the ride experience, I expect it will be earlier and be more about handling than speed, like some modification of the ABS test.