This would be absolutely perfect for WWE although it would never happen - imagine if WWE let Brock fight a few more fights or however many in UFC and Lesnar won the UFC Title again. Imagine he brought it on the show and was carrying around both the WWE and UFC Championships at some point, allowing him to brag about being the most dominant man in the world in both sports. It would put someone over huge if Lesnar lost the WWE Title while still carrying around the UFC Championship. There would be a mentality from said wrestler of "Go back to UFC, because I'm top dog here."
Will never happen that way, but it'd be great if it did.