Guile is the official GNU extension language, so it makes sense. Guile's goal is to provide practical software freedom by allowing more GNU programs to be extensible in the way that Emacs is.
How's that going anyway? It seems GNUcache, Lilypond and TeXmacs are already using guile (and geda also but that doesn't seem to be part of GNU). So make is the fourth Guile-using GNU project?
Because if there's one thing the GNU software-building toolchain needs, it's more languages! How many are we up to now?
Grouping output by target for parallel builds sounds very useful though \o/