This approach is a step up from enigma-reloaded[1] which had some copy+paste friction to use. Genius to put it in the android keyboard itself like an enigma machine.
From a quick glance enigma-reloaded doesn't handle key rotation, which is both mandatory beyond toy usage and hard enough that you can't just send new keys manually. This is why pgp still makes sense today
[1]: https://enigma-reloaded.github.io/enigma-reloaded/#/