Fwiw, Matrix E2E actually exists in separate codebases in: Riot/Web, Riot/iOS, Riot/Android, nheko, matrix-python-sdk, libpurple (in PR), and shortly in Fractal (thanks to https://gitlab.gnome.org/jhaye/olm-rs etc). So yup, it sucks that it's not turned on by default in private rooms, but we're working away as fast as we can.