brainstorming a really smart system engraver

[Kieren MacMillan]

Hello all,

Like many people on this list, I engrave a number of choral works using 
Lilypond. Like a smaller subset of those people, I engrave a number of large 
and very large works (musicals, operas, extended choral works, etc.), which 
require multiple editions (full score, pianovocal score, vocal book, etc.) each 
with their own font sizes, system and page breaks, and so on.

There are many times when two or more of my vocal or choral lines share 
material — for example, in my "Wither's Carol", the entire first verse (with 
the exception of a single two-measure chunk) is in "choral unison" (meaning 
everyone singing the same notes and words in their own usual octave) — whereas 
there are other very contrapuntal sections where material is totally 
independent. Hence, there are sections where a score COULD be adequately 
represented using only 1 choral staff, and other sections that require 2 or 3 
or 4 (or even more) independent staves.

Ultimately, I would like to have Lilypond choose the correct number of staves 
so that horizontal and vertical spacing is optimal, using partcombine (or 
'partexplode'?), cueing, etc., to accomplish its task.

I realize this is an AI nightmare and well outside Lilypond's current scope. So 
as a half-measure, I would love to be able to tag certain sections as "requires 
X staves", and then have Lilypond choose the least number of required staves 
based on system/line breaking. As I [manually] change the line breaks, the 
systems would automagically "expand" or "contract" as necessary/possible to 
accommodate the new layout. Unfortunately, the current tagging system is 
insufficient to do this, as far as I can tell.

Can anyone think of a reasonably easy way to implement this feature?
If so, I'll be happy to sponsor it.

Thanks,
Kieren.