It's a pick em' fight.
Aldo wants to show he's not washed up or damaged goods so he's motivated.
Edgar has always been game and will do anything to win the title.
But if Edgar does win, the UFC brass won't be happy. More than likely Conor won't drop below 155. He'll retire before facing Aldo again or Frankie, losing to smaller guys would really hurt his selling point as an Irish Champion. At 155 or above, the brass can push the "Going up in weight" propaganda to its limit.
Truthfully, Conor isn't exactly overmatched against Frankie. I think Frankie can outclass Conor in technical ability, but Frankie has problems implementing his game against tall, athletic guys. Conor is fast and taller. If they were the same size, Frankie would maul Conor easily. It'd be checkers not chess.
Frankie is in a tough spot because only true fans appreciate his skill, and the UFC would like nothing more than Frankie Edgar, Aldo and Mighty Mouse to disappear. For Dana White it's all about Conor, Sage, Rhonda and Wonderboy. Being the truly best fighter in the world is second to being popular to pay-per-view buyers. It's not like the Superbowl where the champions have to face whoever wins their conference.
