#8 The Big Show

While the Big Show is not yet close to retirement, he has been pretty much a part-time performer for over two years now, due to having to take so much time off to deal with various injuries. After Big Show was absent from TV for just over a year, he returned to WWE SmackDown last October and seemed to form an alliance with then WWE Tag Team Champions Sheamus and Cesaro.
For the next month, they would enter the ring together and Big Show would hold up their Tag Team titles as they pointed to him. The trio then all of a sudden split up in a backstage segment on SmackDown in November, and Show hasn't been seen on main roster TV since.
It has since been reported that Big Show left TV once again to deal with another injury--with his hamstring. Despite this, I still think WWE could have booked Show on the card. He could have made an appearance in the battle royal for a short time, or at least a cameo appearance elsewhere. Any kind of appearance is well deserved thanks to his many contributions to WWE.