Chicago is one of the hottest cities to attend when it comes to pro wrestling. They're not gonna refrain from going there just because some marks are still butt hurt about Punk leaving five months ago. It's not like they refrained from going to Texas when Austin walked out (which was much more of a mega huge deal than Punk leaving was/is.) Never mind how Blue it is to try and "hijack" a show in Punk's name anyway considering he left on his own accord. It's not like the guy was unjustly fired or suspended or something, so I'm not sure what point chanting his name is supposed to prove to WWE other than that a bunch of fans are trying to get themselves over on TV.
And "hijacking" the show with Punk chants worked so well the first time, didn't it? (For the sarcasm impaired - no, it didn't. The Occupy Raw segment with Daniel Bryan a week later was supposedly created to mock the failed hijacking of Raw from the week before, even.)
All that said, if The Shield were being helplessly beat down by Evolution and other random members of the roster and then CM Punk's music hit and he ran down with a steel chair to assist The Shield, that would be awesome. But I wouldn't expect that to happen.
