Developmental state of LilyPond
The official homepage has a notice that reads "Since no developer currently is listed for commercial development, your best bet is asking on the developer list". And it has been three years since the last stable version, 2.18.2, released in March 2014.
However, there is a beta version, 2.19.54, released January 2017, so I am confused. So, there are no regular developers, but there are still devoted volunteers to write code? Does this mean LP is still being developed?
Furthermore, what if LP becomes abandonware in a few years? I do not worry the same for Sibelius and Finale, since there has been a large user base; and even if they really become obsolete one day, someone will certainly write a converting parser for the many legacy works saved in the Sibelius and Finale formats.
Acceptance of the LilyPond format
I worry about this very much, because this leads us to another question of whether the LP format is or will be acceptable in the music circle. If someday I publish my score (though this is absolutely far-fetched as of now), it takes some courage to save one's original work so dear to oneself in a format people seldom use and cannot open, even if LP was (or is) that good. When people publish, publishers seldom let writers or composers edit source on their own, but call for a format they can handle. The possibility is remote that a rare format like LP's will be approved.
Indeed, there is a library that enables LP to import music XML as LP format (see: importing Music into LilyPond from LP's blog). But not the other way around, i.e. LP producing music XML (see possible output formats in LP manual)—this seems to be impossible.
Moreover, my initial impression is that Music XML files are extremely verbose (perhaps for sake of unambiguity?), and one is unlikely to manually edit them. And it is not clear to me that how can Music XML save my tweaking of slurs and other minute details intact.