If Panda is what I think it is (see previous post) then there is a fatal flaw in the whole concept. That is it neglects the direct effect that Google will have on its own results. If it rewards sites that fit the Panda model they will become a stronger fit to the Panda model and the whole thing becomes self fulfilling. As others have said Google just becomes a directory of sites that have been put their by the Panda model that are sustained by their fit to the Panda model that is fed by Google.
Google will end up giving users stuff that they are satisfied with, it might not be the best but they will be satisfied, it'll be OK (just about).
In fact you need a mix of sites in SERPS so that you continue to search and Google needs to provide a mechanism by which new sites have a chance to break in otherwise the Internet stagnates or other search engines take over because their is a basic human need to explore.