If you're interested, feel free to either send a PR or fork the module and start your own, whichever you prefer. I'm perfectly fine with either: that's why my modules are open source. If you'd also like me to add you as a contributor on the Xposed repo, please let me know.
I wrote a script (it's a shell script and isn't the most readable) to find obfuscated methods. It works for most methods (last I checked) but is no longer enough for changing the quality, so you'll have to figure that part on your own. You can find it here. If you can't run it, look for the "grep" lines and let me know if you can't understand it.
A quick tip to figure out which method to hook for changing the quality: hook View.class's onClick method (if memory serves right -- might be onTouch) and figure out which class the video player's quality button belongs to. Then hook all methods in that class, and work your way backwards to see which method is actually responsible for changing the quality. A *lot* of methods will be called for each step, and many of them will require you to look at many other classes or parent methods to finally understand what each does, but this will hopefully help you get started.