1 - He Could Return As UFC Heavyweight Champion
Even though Daniel Cormier is one of the greatest fighters in UFC history, it's definitely possible that he'll lose his heavyweight championship if he ends up inside the octagon with Brock Lesnar next year.
If Lesnar does end up regaining the UFC heavyweight championship, it'll obviously make him a lot more valuable to the UFC, and it'd make him even more valuable than he already is to WWE simply because they've never had an active UFC champion on their roster.
Also, Lesnar could end up being the first person ever to hold both a WWE world title and the UFC heavyweight championship simultaneously. It'd also help him get more money from WWE, as him coming back to the company as the UFC heavyweight champion would be a huge deal.