In the context of the long discussions of what does lilypond need to do, I'm predisposed
to try to think about it in terms of what (I think I) know about TeX/LaTeX.
So the first question is: how much of lilypond's goals and design are based on TeX/LaTeX?
Along these lines comes a series of other questions:
Is "what you see is what you mean" input is the goal?
Is there the same TeX=detailed typesetting (engraving), LaTeX=hides users
from the details of those details (mostly) concept for Lilypond?
[I believe that this is one way to roughly characterize the difference]
For me, working with beamer is a different experience from writing out an article,
maybe there will (or could be) as much difference in the way that the text
input is organized and used in different forms of musical documents.
We're starting to see some of this division of labor -- several of the contributors
to the "what does lilypond offer..." thread have already made significant contributions along these
lines, building on top of lilypond itself.
Anyway, I'm starting to ramble into other points.
Dave