Sorry but I just fundamentally disagree about the app centralization.
If you want xmpp to gain traction you need an app that exists on both mobile platforms. It can (and should) have per-platform tweaks and everything to be performant. But a person needs to be able to just tell their friend a single app, they need to be able to find it in their app store.
The question is "how does xmpp gain traction?" and the answer is having a single flagship app that runs on everything.
If you want xmpp to gain traction you need an app that exists on both mobile platforms. It can (and should) have per-platform tweaks and everything to be performant. But a person needs to be able to just tell their friend a single app, they need to be able to find it in their app store.
The question is "how does xmpp gain traction?" and the answer is having a single flagship app that runs on everything.