Anderton
The biggest difference if you upgrade now is that instead of getting only the features that were added since X3e was released, you get those features and a 12-month membership where you receive features, content, tutorials, etc. for the next year. Anything you acquire during the membership does not expire. You can pay all at once, or spread out the payments over 12 months.
At the end of 12 months the membership itself does expire. If your membership expires, you won't receive new updates, features, etc. unless you renew - in other words, Cakewalk will continue to do yearly paid upgrades, like going from X1 to X2, X2 to X3, etc. However if you don't renew, everything up to that point is remains fully functional and permanently activated. It would be as if you had X2 but didn't upgrade to X3.
This is not like the Adobe or Avid programs. You keep what you buy.
I have only called Cakewalk 2 or 3 times over the years and not for product support issues, but my assumption was that if I had a product operational issue with, let's say, Sonar X1 today, I would be able to get some level of phone support if needed (although, I reckon the issue would more likely be solved by checking on the forum).
My question is, with the new membership model going forward, is there any change in the support model for the version of Sonar you own if your membership ends or if it has lapsed?