There's some interesting stuff on that Flickr group - I might have to start visiting it occasionally!
I was actually thinking along the lines of a 26" or 700c front end with a 20" rear grafted on. It'd certainly look ...er... distinctive, but I wonder if the handling would be a problem. Specialized used to do a version of the Big Hit with a 24" rear wheel, and I've seen a few 96er and 69er MTBs, so differing wheel size can't be a problem
per se. But would an '06er' be a step too far, I wonder?
I suppose I'm going to have to find out the hard way, now I've mentioned it, eh?