Mike Singletary is an alum and if not for that I wouldn't want him and I'd think that's the only reason his name is out there.
The other 2 are possible, both are from Texas and can run an up tempo offense like they have been at Baylor. I'd say Phillip Montgomery too but I'd guess they'd want a complete break from Briles' regime. Maybe the Arkansas State coach who was Fedora's OC at UNC.
I think Les Miles could be a possible too. He's coached at Ok. State and from his comments he's open to a more modern offense now. He coached in the B12 and did hire Mike Gundy at Ok. State so it's not like he couldn't hire a coordinator like that and he hired Dave Aranda too on defense at LSU so I think he is capable of hiring more creative coordinators.
If it's someone without HC experience, I'd wonder about one of the TCU coordinators specifically Doug Meacham.