I'm a lilypond user and I can tell you we're totally spoiled by the quality of that project - it is just immaculate. The Vexflow samples look very primitive by comparison but it's a great idea and with open work like lilypond already having tread this ground, hopefully they will have a lot of resources going forward.

Have never come across LilyPond before (for that matter I haven't used any software in that area since Sibelius about 5 years ago), but that looks amazing. Thanks for linking to the essay, most interesting thing I've read in a while!