Was it really unexpected? Likely not. Punk has not been a happy camper within WWE for quite some time. That point has been made abundantly clear on many occasions. He's tired, he's beat up, and he's not enjoying himself at work.
Matters such as this generally concern one or both of the Two C's….cash and/or creative. Punk is mentally and physically burned out and he's not having enough professional fulfillment to work through his issues. He needs a break.
Punk is a very cerebral talent who has earned his stripes the hard way and has more than paid his dues. He's earned super star status via having numerous, main event classic bouts in WWE rings on huge stages. Coming to WWE was the greatest thing Punk could have done for himself professionally. He's become globally famous and has made a handsome amount of money thanks to the WWE machine.
I do not think that Punk has wrestled his last match in WWE. I do feel that it's best for all involved for Punk to take much needed time off even if it means that he misses a WrestleMania.