Landing MusicXML export summer of code work into LilyPond?

[Paul]

Hello Davids Kastrup and Garfinkle,

Since we will soon be losing David K. to more lucrative pursuits, I 
thought I'd ask about the status of David G.'s summer of code work on 
MusicXML export.  I'd love to see that land in LilyPond (at least the 
part to generate an SXML file which could be manually post-processed to 
MusicXML with Guile 2 until LilyPond makes the transition to Guile 2).

What needs to be done and can I help with making it happen?

(Not just theoretical interest, as one of my bandmates uses MuseScore 
and would like MusicXML versions of my LilyPond files.)

Cheers and thanks,
-Paul