The very latest word coming from backstage in WWE is that The Undertaker and Kane vs The Shield is not a definite for SummerSlam. While the match has been discussed, it all depends on whether or not 'Taker is wanting/able to compete.
As we noted before the current "Plan B" in WWE is for Brock Lesnar vs The Undertaker to take place at WrestleMania 30 if Rock vs Lesnar doesn't happen.
It's also a possibility that The Rock could be involved in the McMahon family story line, which could continue as far as WrestleMania 30.
In other SummerSlam news, most WWE officials are certain that Daniel Bryan vs John Cena for the WWE Title is a lock for the PPV, and there are said to be quite a few Bryan supporters who are pushing for him to win the title.