"medley" should be an attribute of the "performance of" relationship instead of its own relationship. There is no way currently to relate a "live medley" performance, other than creating two separate ARs.

original proposal wiki: http://wiki.musicbrainz.org/User:Hawke/Proposal/Performance-medley

New wikis:
*http://wiki.musicbrainz.org/User:Tommycrock/Performance_Relationship_Type
*http://wiki.musicbrainz.org/User:Tommycrock/Medley_Relationship_Type

Once this attribute is created, all "medley of" relationships should be migrated to the new attribute. The wording should remain "medley of", "live medley of", etc. instead of "medley performance of", if possible. The join phrase should become:
*is a

{partial}

{live}

{instrumental}

{cover}

recording of

{medley:a medley including}