Book 2 has a partial Android build. The problem is that Android needs to stick <2GB for the base app, and Book 2 is 5.4GB. I can side-load some stuff (images), but when I set up that system it didn't support videos (of which there area lot of in Book2). So even with all the images downloaded separately, and with video resolution reduced, I'm still at 2.5GB, and the app crashes on start.
I'm trying to work out a solution for that, but... that's why there's no Android build atm.