I actually have no problem with him being in it. This is my thinking (if it proves to be wrong, I take it back): if they are really stretching the feud out til Summerslam (which we all hope, although I've been reading Big Show/Punk rumors, hopefully that isn't true), they need to stretch it out for three more ppvs. Might as well add someone to one of the matches to continue to stretch it out so that it doesn't get as stale (Christian vs. Orton went from Over the Limit to Summerslam last year, and by the end, it definitely was getting a little repetitive). Kane being in it allows them to do something with the finish that still isn't decisive, leading to more later on. Now, if they end the feud shortly after this one, or make Kane the focus, I take it back, but for now, I think that in the end when we look back on the entire feud, it will be fine.
Plus, the addition of Kane has actually made a lot of sense and has been pretty well done.