Nor forgetting the 8.1 RTM ability to boot straight to the legacy desktop, as a choice..
Classic and start8, are both compatible. Personally I would not see the point of paying for something which has free alternatives doing the same job.
Start8 and classic are in the store, so I don't really see them vanishing in a hurry? Like many other earlier programs, there are better alternatives than the built in ones (Paint, for example). Microsoft have never, historically, obstructed their use.