This is 0 information and just a gut feeling but my sights are set on someone either from the NFL or some kind of NFL influence. Last year it was all Joe Brady, Dorsey, and Coen (1 year removed from the NFL) until Gattis came into the picture. The college guys were quickly weeded out because they ride coattails of guys like Heupel, Riley, Dykes, etc.
It's easier to vet NFL candidates because teams aren't holding guys back from "promotions" to OC even in college and you have connects in guys like Zo who knows everyone. Mario is also tight with Darren Rizzi and Dennis Allen from the Saints, McVay, and others at that level. It's a lot easier to vet and get feedback on those guys.
I'd be surprised if the OC isn't in that mold: Joe Brady, Dan Pitcher, Shea Tierney, Rob Calabrese, Drew Petzing, Parks Frazier, David Girardi, Bo Hardegree, Kevin Patullo, Brian Johnson, Andrew Janocko, Chris O'Hara, TJ Yates, Ronald Curry, Cam Turner, Spencer Whipple, Jake Peetz - only a few of those guys have legit reasons to hold up any longer because they're still playing.. some still in the conversation for NFL OC jobs. Could be another reason.
Also wouldn't be surprised to maybe pivot to seasoned NFL vets that aren't coordinating an offense right now similar to Georgia hiring Monken - Greg Roman, Freddie Kitchens, Darrell Bevell, Mike McCoy, Jay Gruden, Greg Olson, etc. - doubt many/if any of them would go for it aside from maybe Freddie Kitchens who is on staff at USCjr