The reason I'm wondering is because I'm trying to figure out if these types of chord subs. could be used as pivot notes in which you could then modulate the music with, in order to write something such as a fugue, where you have a subject phrase and then one or more phases that answer to the subject.
A fugue incase you're wondering has a pretty good definition here
http://en.wikipedia.org/wiki/Fugue
if you listen to the samples on the site they are pretty good. In fact another way I've heard people describe a fugue is that there will be a central foundation of the music and then two or more voices will play completely seperated parts around that one central foundation.
Could there chord substitutions be used as a way of having two voices play around the same peice and how would one be able to farther away from the central foundation and with them and back again?