10. WWE's Pay Scale Blown Away
Conor McGregor is a man obsessed with money. He talks about "business" as much as he does the sport of MMA. Dana White even noted that McGregor's biggest motivation is money, hence why he thinks he'll return.
So there's no way McGregor goes to WWE for less than ten million dollars. That's around about what he could earn from one fight in UFC, and he'd aim to fight three or four times a year in MMA. His earning potential in UFC is extraordinary.
So Vince McMahon would have to upset the WWE pay scale. McGregor would be on more than Lesnar, maybe even more than Cena. But then, this is a guy doing close to two million PPV buys. He's a mainstream asset. He could be worth it.
WWE's locker room wouldn't be happy, but McGregor would be in for around $15 million, on a Lesnar schedule. In term of deal length, two years would make sense, he doesn't want to tie himself down for too long.