I am assuming that the idea is to leverage the recently released web interface by whatA$$isUp to be able to interact with an xmpp client.
I see some issues:
Since it appears that to gain registration of the web interface one needs to have whatA$$isUp installed on the device it would not save users the pain to have the apk installated at least for initial registration on the web interface or account setup.
After the web interface has been authorized , running the server running the bridge, Disroot would be responsive for the security of the users making itself a target for security breaches.
… and for some service that wants to create a space away from the big tech radar as much as possible, and betting that the terms and conditions of whatA$$isUp service would prohibit any hacking, the admin of the server would be exposing to cease and desist letters.