I think it makes a lot of sense, but it all depends what you want from a DAP, so it won't suit everyone. I do all my wireless file management, ocassional multimedia, and dedicated streaming/local hi-res music listening from my DAP, so I want a modern Android platform with a 1080P+ display, fast WiFi, networking support and good ergonomics. If all you want is a small player with limited features and a minimalist approach, there are .any other options on the market. This just won't be one of them.
PS. With open Android you really want to be using UAPP, not the stock player. Be it Shanling, FiiO or HiBy, UAPP is leagues ahead of all of them in features (including gapless), UI, speed and SQ, not to mention streaming integration. The M9 should be able to run UAPP very smoothly indeed, which solves any player issues you might have with Shanling.