Doesn't using this with Discord run a risk of your account getting banned for using a third-party client? That's why the Cordless developer shut down the project: https://github.com/Bios-Marcel/cordless
It never used to be like this. MSN messenger,AIM even YIM; they all had FOSS applications.
Discord's generally fine with anything using it's API/gateways as long as it's NOT logging in as a "real" user.
So I imagine there might be the possibility of it being allowed for Beeper as well.
The broader question of whether bridges are allowed seems to be broadly yes as there are many other bridges out there for Discord (IRC/slack ones) and those haven't been shut down either.
I think so long as you aren't abusive, Discord don't care.