Michigan isn't going to play another neutral site game any time soon, if ever. They have their big non-con games scheduled through 2027 with series against Washington, UCLA, Texas, and Oklahoma.... Hopefully they'll announce 2028/2029 soon, because schools usually have those set up 10 years in advance.... USC and Tennessee appear to be two of the best possibilities if FBSchedules.com is accurate.
My bigger concern is that the guarantee games won't be as good in the future. Bill Martin was lazy about them, but Dave Brandon did a good job with scheduling home games against the likes of Air Force, Cincinnati, SMU, UCF, Oregon State, and BYU..... So far, Warde Manuel has settled for MAC, CUSA, and SunBelt teams, except for Colorado State.