1. Money (Because That's What's Really Best For Business)
It's all about the Benjamins, period. That's what is best for business. And if the WWE, or any other pro wrestling or MMA entity, thinks it can make money off the MMA/wrestling crossover, then it needs to do it. There's no way bringing in someone like Ronda Rousey, even in a cameo, wouldn't generate tons of interest. Brock Lesnar, despite his huge paycheck, moves the needle every time he shows up on WWE programming. There's never a time when Lesnar appears and fans aren't talking about it. Pick the right guys (or girls, such as the Four Horsewomen) and run with it. Because in the end, it's best for business. It brings in the money, and that's what the business really needs.