Membership gives access to a year of new features and bug fixes. This is approximately the same (or better) as the previous deal where you would buy the "latest version" and get about half a year of patches, with the next major version coming out roughly a year after the current one.
I would assume that if new features are added over the course of a year, new bugs might also find their way into the software. So after a year you might be left with a few. This is not any different from what happened with, say, X2. However, the CCC supposedly makes it easy to roll back versions. If your membership expires in August and a bug from July was not fixed, you should be able to roll back to the June version (just as an example). That's actually better than it has been up till now.