actually, nevermind. I see (at least on android) that all this bacially is a webview of the default mobile interface. (which works quite nicely by the way...)
There's more in there than just the webview: all the push channel and notification stuff, a JMAP client, a Gravatar client and cache, sharing stuff, smartwatch hooks, etc. That said, none of it is particularly interesting or difficult.
No plans to open source it at the moment, but we might if there was sufficient demand.