Costa or Rob would be a mistake because if Khamzat loses, they don't get Izzy rematches for it. They're better off fighting each other, trying to build back towards an Izzy fight.
Maybe winner of Brunson - Hermansson, though I do know he's trained with Joker before (and grappled against him too). Brunson's been on a good run since losing to Izzy, so he may actually get a rematch, and Joker never fought Izzy either, so that could work as an eliminator. Or even Strickland if he recovers soon, I imagine the build up would be crazy
Or if the UFC wants to ensure a new matchup, go crazy and book Muniz vs Khamzat, winner gets Izzy. It's a long shot as a contender, but the division is basically devoid of them