GUILE2.2 from master takes eternities to compile, like more than half an
hour or so. LilyPond does a lot of on-the-fly evaluation, and Guile2.0
is already a big step backwards in that department compared to Guile
1.8.
If they don't get compilation and partly interpreter speed under control
again (and it does not look like a priority to them since they are more
interested in competing on the basis of compiled code speed), the main
usability focus will be _not_ as an extension language but rather as a
main programming language.