It's really hard to disagree with anything Frank says here:

“When I realized we would have to cancel the show, I said, ‘Look, I’ll fight the guy. You know, it’s a great story -- little brother steps into the spot, comes out of the booth. It’s very compelling, but we need a fight to happen that’s compelling,’” Frank said. “That went around for hours. Then I put my shirt on and went to work. No one committed to it, so I just kept talking.” 

“Kimbo is great, great for ratings,” he said. “But Kimbo fighting a star, a superstar, somebody who’s going to elevate him or knock him down in a good way … that’s what we needed that night. We didn’t need a nobody to beat Kimbo.” 

If Frank had fought and beat Kimbo, you'd have all sorts of opportunities going forward: A rematch down the line once Kimbo improves, a casual fan dream match against Ken, or a big rematch with Tito Ortiz.  Frank would have been a big star overnight.  Instead I think it's most likely we have a guy that will lose his next fight unless it's against Kimbo again, and I don't think he has any star potential for CBS.  It will go down as a gigantic missed opportunity to turn Frank Shamrock into a second marketable star in addition to Kimbo Slice for the promotion.