Nice feature ! - Great !
Is there also planned to implement this for other formats which have a gaining-function like MP3, Vorbis and FLAC ?
AFAIK, only MP3s with a Lame Header after 3.94 have native ReplayGain support.
Just try the placeholders %replaygain_track_gain%, %replaygain_track_peak%, %replaygain_album_gain% and %replaygain_track_peak% to get ReplayGain information from the Vorbis Comments or ID3v2/APEv2 tags.
Okay, this means then that these placeholders are not only suitable for MPC, but also for the other formats like Vorbis and FLAC (´cause FLAC also uses Vorbis-tags, right?).
Please note the difference between
%replaygain_track_gain% (Tag field name, supported with every format)
%_replaygain_track_gain% (Tech field directly from the Musepack header supported at Musepack files ).