The legal framework for a private company doing it is already there. At least in the US, you can always cancel with a properly worded certified letter to the company. You would probably need to give the company limited power of attorney to send the letter on your behalf. This isn't as crazy as it sounds, its essentially the same thing as title companies. You give them power of attorney and they deal with the DMV for you for things like transfering title of your car.

Having said that, I don't think the market for painless cancelling is big enough to do this given the legal overhead that would be needed.