I have published one complete work in Lilypond which I estimate has been downloaded about 50k times (and those downloads were probably reused for multiple people, because it was an instructional work). I guess that qualifies me to answer?
* I have a background in LaTeX, so that's why I picked it up. The work I transcribed is a set of six French baroque sonatas for two violins which are commonly used in intermediate-to-advanced teaching.
* At the time I did it, there was no freely available score that showed both parts on the same page, just reproductions of the original handwritten manuscript, so I did it to have a cleaner copy where you can see both parts at the same time. I had to edit slightly because it turned out the original contained a handful of errors.'
* Very similar. Lilypond started life as LaTeX macros, and while it's now well beyond that, you can see the roots. Lilypond can output MIDIs from source.
* I don't know about git repos, but there's no reason you couldn't. I did publish the source alongside the finished PDF on IMSLP (the International Music Score Library Project, a wiki of public domain music).
* For my purposes (playing European music using the 12 tones in the traditional style from Renaissance to modern, both classical and folk), perfectly expressive. I'm not sure what you mean by abstraction in this context, but if you want to do something for which there isn't common notation, you can just write words.
I would use Lilypond without hesitation if I had a new work I wanted to publish, just as I would use LaTeX to publish a book or document. It's a typesetting system, and if you're using it, you're already committed to the form of traditional European sheet music.
* I have a background in LaTeX, so that's why I picked it up. The work I transcribed is a set of six French baroque sonatas for two violins which are commonly used in intermediate-to-advanced teaching.
* At the time I did it, there was no freely available score that showed both parts on the same page, just reproductions of the original handwritten manuscript, so I did it to have a cleaner copy where you can see both parts at the same time. I had to edit slightly because it turned out the original contained a handful of errors.'
* Very similar. Lilypond started life as LaTeX macros, and while it's now well beyond that, you can see the roots. Lilypond can output MIDIs from source.
* I don't know about git repos, but there's no reason you couldn't. I did publish the source alongside the finished PDF on IMSLP (the International Music Score Library Project, a wiki of public domain music).
* For my purposes (playing European music using the 12 tones in the traditional style from Renaissance to modern, both classical and folk), perfectly expressive. I'm not sure what you mean by abstraction in this context, but if you want to do something for which there isn't common notation, you can just write words.
I would use Lilypond without hesitation if I had a new work I wanted to publish, just as I would use LaTeX to publish a book or document. It's a typesetting system, and if you're using it, you're already committed to the form of traditional European sheet music.