It needs to be remembered that autofuel STC’s are available for some higher powered engines not normally associated with its use. The Baron and 210 are both approved for 91AKI minimum. Yes they require mods (ADI) but approved nonetheless. If the FAA would not have played favorites when they were doling out the cash, the problem would have been solved 25 years ago.
You can shave up to 13 octane points off an engine by using water/methanol injection. So it’s clear that one would not need 93, and that even Swifts 94 would be overkill if ADI is used. AOPA said a few weeks back that they would test any fuel in their Baron that showed promise. Well the Baron has been approved for 91AKI since 1988. I’m still waiting for a call from AOPA.