Surely, no company would force you to subscribe to a version you already own. That would just be a serious slap in the face. And, my suggestion to CW would be they continue offering a full-price retail version you can buy outright, but for those who would prefer to "amortize" their purchase, they could through a subscription model. The difference being, that the retail users would be required to purchase newer versions at the upgrade price, while subscription customers would simply download and install the new version at will.
btw, I suggest the subscription model offer a slightly more expensive "all-in" option to use literally everything CW offers, including the training materials.