Emacs not being usable on mobile is a big problem and biggest roadblock in the path.
In principle you could add special Android bindings for emacs which would make using it without a keyboard somewhat useful.
Mobileorg was that app for a while but it's development stopped and it's no longer usable.
That's one of many hidden strengths of Emacs-based workflow - it works the same whether you're running in GUI mode, or connecting remotely with text terminal. That also means I can work on heavy projects from my underpowered 2-in-1 netbook :).