Can we involve Cerrone somehow?
Seriously though, even if it was established the fight would be at a catchweight, doing that fight would be less beneficial for everyone involved than literally doing nothing at all.
UFC has 2 ready made contenders who have decent win streaks and records against their divisions, and can headline 2 pay-per-views with both men. If you put them against each other, and one loses, you have just thrown money out the window by snapping a win streak that would sell more tickets than having to make either guy start from scratch.
People like the movie better if you don't pull the curtain back, ya know?