Funny how you mention that when i also say in the post. To be honest playstation vita has the playstation mobile games which were sony xperia type games on vita. I see no reason why they shouldn't port the mobile games to switch (or 3DS) In fact is probably more of a reason. Also it could use eshop money instead of android money to pay for content (If they wanted) Or a full paid version with all content accessable. Still is possible and no reason why it can't happen.Its not all Shield Branded devices, as to why you can't on Shield Tablet, idk, but Shield Portable it installs fine. I'm not into it enough to care to play, but it does load up, and install from the app store just fine. Games like this however very rarely make it to Shield TV though
Edit: They could also be planning to bring this to the Switch, and having this on Shield Tablet and Switch could be like competing against itself... idk honestly
Personally i didn't like the idea of nintendo making games for smartphones anyway but now is probably gonna work for them. I just want to play game with buttons not touching a screen.