There was a "Ladies and Gentlemen" mail sent out about playback on the Pono sometime around ~2014 if memory serves.
There wasn't actually a Hell of a lot that needed doing to the Android port in general to get it to run in the crippled environment that is a Pono (I'll touch on that more if prompted to), and I don't think any of it ever hit our sources because the guy working on it ended up bricking his player and the level of regard for that fact was truly minimal.
The crux of it is, basically, that it was a combination of two pretty terrible ideas (Rockbox as an App on Android, and the Pono player {I'll touch on that too, if prompted to, but since you backed it I'm not sure you want me to detail the wide and varied amount of ways it was a truly terrible idea}) slapped together to make one giant terrible idea.
But no one is going to stand in your way.
EDIT: The NewPort wiki page isn't particularly useful here, though it isn't entirely useless. It isn't entirely necessary to have a wide understanding of the hardware when running hosted - however if you intended to replace the operating system entirely, that changes a lot, both in the necessity of the steps detailed on that page and the sheer amount of work required to reach the end goal.
[Saint]