I definately think Colorado needs to go. Wether they ever get themselves a goodteam is irrelavent. They are cheapshot artists who have classless fans.
HOWEVER I wouldn't want to replace them with a school like TCU, The conference is already Texas heavy enough, bringing in TCU would give the Texas schools even more leverage when negotiating things such as conference championship venues and things like that.
Also wouldn't want a team like Hawaii as that makes travel issues for the team durring visiting years, its not a marketable game and theres no recruiting base to be won for any current big 12 school by bringing in a team from so far away. I'd much rather bring in a Minnesota or a Illinois which are closer to the nexus, though my first choice would actually be a school like Cincinatti. With a bigger conference with a CCG and a BCS bid to draw players from that good Ohio talent base they could be a good team for the North.