[tjr]

For some arenas of music, such as jazz combo-oriented groups, a very basic melody lead sheet with chords and song structure elements (section a, section b, repeat, etc.) is plenty.

Maybe rather than focusing on building a full music notation system for the web, focusing on making something for lead sheets / rhythm charts / etc would be a better path. I really don't like breaking out Finale to do jazz rhythm charts, but right now it's just about the best option. Make something better, and I for one would pay for it.