I can see why the developer doesn't bother: the UI would need to be very different. SmartTube is meant for use on TVs, not on touchscreens, so it has no touch UI at all and is designed for use with a remote control. There's some other apps that basically do the same thing, but on Android mobile, such as ReVanced I think.
ReVanced is patched up original Youtube (which has among other things the benefits of not showing ads), but the equivalent to SmartTube would be NewPipe, which is a new YouTube replacement app.
It would not - NewPipe and its derivatives don't support Youtube accounts unlike SmartTube. With SmartTube (and Revanced, on Android mobiles) you can sign into Youtube and use your playlists, likes, comments etc.
