With commit 32e89926db, media-tv/xbmc-9999 can now be built with optional libplist support.
should be all set now in the tree; thanks for the report! Commit message: Make plist depend into USE=airplay http://sources.gentoo.org/media-tv/xbmc/metadata.xml?r1=1.8&r2=1.9 http://sources.gentoo.org/media-tv/xbmc/xbmc-9999.ebuild?r1=1.89&r2=1.90