You don't need openweight for that, just catchweight & that can and has been done before so whats the problem?
But having more than 1 weightclass different would by most people be called a freakshow. The problem with the mentioned fights are that either the UFC and/or the fighters won't do the particular fights, not because of the wieght.
well thats just annoying, i enjoyed wandy-cro cop and other fights like that in pride, i wish they would agree gsp wont even face silva who is a weight class above him. but you cant say any fight with bj penn in it is a freakshow because he holds his own against machida at heavyweight and people at lw and ww