I got hit by this. As soon as I reloaded Mail.app after installing the last update I was presented with two options, "Start trial" or "Buy now", neither of which I want. If they did mention mandatory registration in the release notes then they didn't make it clear enough.

I don't mind buying software that I use, but I completely object to having working software pulled out from under me like this.

Nasty surprise this one. I don’t mind paying for a good app, but for software that got lots of donations to keep it opensource: switching to CS with a €24 fee is really steep and feels like nothing but greed and screwing donators over.

Well, even though I had it installed, I never really used it.

Does this change anything with GPG Keychain?

this was an unfortunate surprise.