Hi, the idea of a keyboard for autofill in Android apps is great (more because in Android 4.4 the notification mode for autofill is not supported), but it's not very handy to change keyboard every time I need to autofill, and the Enpass integrated keyboard cannot substitute a full Keyboard app (with multiple languages, completion, prediction, and so on....).
I think you should take into consideration a partnership with a keyboard app developer, in order to integrate Enpass feature in a full Android keyboard (maybe with a "plugin app").
An example should be SwiftKey, a very good keyboard now free to install.