I have so much content I bought from iTunes during my Apple-using years, and it's been annoying that all that content is worthless when I'm out with only my Android phone on hand. Well done, Apple, if they launch this app.
Edited to add for those not in the know: you can use MoviesAnywhere to get your movies onto Amazon Prime and other services, but your TV shows do not transfer. I was fully devoted to Apple for over a decade, and spent thousands on content (music, movies, tv shows, etc), and I want to be able to use what I paid for, even if I'm not still using iPhone.