Ionic v1 support and expiry

With Ionic v2, Ionic v3, are the Ionic framework developers still going to release fixes and enhancements on Ionic v1?
What is the actual date when Ionic v1 will be closed/terminated by framework developers?

Fixes yes, enhancements and new features are less probable.

Ionic Framework 4 will bring new functionality that will probably enable you do use new Ionic 4 stuff in Ionic v1 projects - but this is still not sure and locked down.

No plans are known for this. Ionic v1 works quite well, Ionic CLI and Cordova CLI are kept up to date so you are getting updates for the native app part that might be required by new OS versions.