There's been talk that the UFC would bring in somebody who's either 0-0, 1-0, 1-1, or 2-1. He won't be fighting anybody of note, so expect him to be babied as much as possible, ala Herschel Walker in Strikeforce.
What is bad about having Punk actually fight in the UFC is that it greatly degrades the quality of the product. The UFC always touts how they are on par with top sports leagues like the NFL, NBA, and MLB when it's convenient for them (like banning all outside sponsors for fighters next year so their fighters have to wear Reebok uniforms) but a move like this completely goes against that.
In what other sports league can a guy with no competitive athletic background just be allowed to come in and be an active participant because he does some training as a hobby and is a really big fan?
This is just like when celebrities come into to "try that wrestling stuff" because they've seen it on TV and thinks it looks like fun.