Let me help clarify everything:
PhoneGap Build: shutting down. That is what the email was referring to
PhoneGap CLI: no longer maintained. It was a fork of the Cordova CLI
PhoneGap Developer App: no longer available
PhoneGap Desktop App: no longer maintained. Source code available
Cordova CLI: Active and maintained
Cordova/PhoneGap Plugins: No change. Depends on the plugin author. The Cordova team is still maintaining the ‘core’ plugins.
If you are building with Cordova, which Ionic has traditional done you are fine.