I'm not sure how well these would work, but at least here in China, it is slow to wait for previews of musical scores for each modification. If you could add client-side support to Score, perhaps via:
...I wonder whether client-side rendering support (ideally in SVG in case notes could be synchronized with the music play-back in the future) could be added, if not now, then maybe after the main Mediawiki WYSIWYG interface stabilizes?
And support for the emerging Web Audio standard would be awesome for client-side audio play-back as well...
Also, with ABC seeming (to my quick glance) more like an open standard than Lilypond, might it make sense to make ABC the default?