Re: Any kind of central "real world identity" system is RIPE for abuse. Period.
You don't need anything apart from the Android app to start using it.
Presumably you need at least one interlocutor.
And therein, I think, lies the rub. I haven't produced any content on Facebook since shortly after I first signed up several years ago: not a post, not a status update, not a "like". I do, however, read it for at least a few minutes most days, because my extended family and friends post heavily, and I respect them enough to try to pay a bit of attention.
None of them are using Delta Chat. None of them are likely to ever start using some new decentralized IMAP-based social media system. True, several use Twitter or Instagram or god knows what else; I ignore all of that because the Facebook skim is all I'm willing to invest in this, respect or no. But they started using those other non-Facebook social media services because there was pressure to, and that pressure was largely generated by marketing campaigns.1
I've yet to see an open protocol with a real marketing campaign.
To the vast majority of ordinary users, a new social media service is just what they see in the client app. And if that doesn't do something that they see as novel and valuable, they won't adopt it.
1Typically "stealth" campaigns of the sort described by Holiday.