You can, but it's not an infinite energy machine, the increased resistance to moving forwards is going to suck more energy out of the first vehicles battery than it is going to put into the second, your total range will be strictly less than if you didn't do that.
You have 0% energy added by having one Model x/S. How impractical it is, fine: but, the fact you might be able to do it in the future gives model y’s cars the better decision over one Model X/S
