It's highly unlikely to happen, but wouldn't it be something if they called upon some of the classic hosts to fill in for Meredith? I can see either of the brothers Narz, for example, doing a fine job with this. Also, since they seem to value host-contestant interaction highly on the daytime show, even Bob Barker--now there's a really long shot (and yet another T.K. reference)--would be a good choice.
Yes, I know: ain't gonna happen. It does, however, have the advantage of not putting in Meredith's shoes anyone likely to be auditioning for the job on a permanent basis.
EDIT: By the way, what was the last game show to employ a substitute host (other than for April Fool's Day stunts on WoF and J!)? Was it The All-New LMAD?