Am I understanding correctly that this is mainly for positioning lyrics for playback during repeated sections? Such as adding lyric events at the right place in a standard MIDI file?
If that is the use case, then I think we could do this by adding a time-only attribute to the lyric element like we do for other elements. If you agree, could you please add this as an issue at the W3C Music Notation Community Group's GitHub site for MusicXML?
If I am misunderstanding something here, please let me know.
VP of MusicXML Technologies