I'm actually shocked that some people claim to be actually likely to
cancel their subscription over this. Really? Really?
I can only assume they misunderstand what's happening to the subscription. It's not going away. You're not paying more for it now. It's not taking content away from what you're already paying for. What it
is doing is giving you notice that soon (nearly two months from now) the subscription price will be increasing for everyone subscribing or extending after that date, and that if you want to sign up for an additional year beyond whatever you've already paid for, the next 45 days are the best time to do it. They also noted that they're planning upon releasing new D&DI Tools, upping the page-count of Dragon and Dungeon magazines, and giving exclusive, playable previews of next year's releases beginning a full nine months in advance of release, and that this preview content
will not be included in the newly-increased page count of the magazines.
Mark me down in the m'eh column.
If the amount of original content shrinks due to these previews... then it goes from m'eh to "might be time to cancel."
They have explicitly said that the PH3 previews won't be taking up space in the magazines nor detracting from the page counts of them, AFAIK. I've also heard rumour that each preview will be accompanied by a companion article in the magazines, which will build upon the material presented in the playable previews*.
(*It's important to remember that these aren't playtests; they're previews of completed material.)