I wish that's a feasible business model considering the amount of research and funding goes into development of FSD.
Currently, FSD is tied to the VIN, similar to OEMs tying OS license to a laptop. If you sell the car, the new owner get FSD. If your car is totaled, bad luck for you. FSD is not transferrable to your new car. If and when Tesla starts subscription model, it'll be use and pay for a specific VIN, probably with no contract. If your statement of tying FSD to profile and use it on any car is definitely not possible... If so, Tesla will still make you pay FSD payments based on no.of cars in your profile... it's not a pool of floating license(s) that you can use on any car.. I don't think Tesla will ever go down that path.