I can see two arguments to this. Keep it classic and separate, but at the same time, you have earned these pieces and live server toons should have them as well. Thoughts?
EDIT: I am referring to gear that you obtain on Classic servers, allowed to mog on Live servers, not sending anything to Classic servers. It would just add gear from Classic to be added to your appearance tab on LIVE servers.
EDIT 2: I AM NOT SAYING CLASSIC SHOULD HAVE TRANSMOG OPTIONS.