The people at XDA are always doing out of the ordinary things, especially when it comes to Android. Other times they implement changes that makes you wonder why billion dollar companies aren’t doing it in the first place. This time it has to do with 720p playback on just about any Android device, including devices with lower resolution. XDA member theos0o has released that mod and has written instructions on how to achieve it (in the second source link), furthermore by using the correct mod you can have true 720p playback over a mobile data connection.
It might seem odd for users of older Android phones with low resolution to want this, but apparently users are claiming higher quality streaming anyway, better than the built in “HQ” setting in the original YouTube app.
Source: XDA-Developers, XDA Mod Post