It's not that easy with emulators - different emulators may have a different accuracy, system requirements, features or support (for example NES has different mappers - some mappers are not supportes on some emulators). So for some systems it makes sense to put more than one emulator into the repo (of course the reasons should be mantioned in the package request ;) ).

I know but the performance via Nuvola Player is quite bad and it has several graphical glitches (it is even still using flash...I mean...come on...).
GPMDP on the other hand runs great, has more features (last.fm tracking, mini player, equalizer etc.) and is well received by Google Play Music users.