[jgust]

That is the theory behind "flex fuel" vehicles. In practice, the optimizations don't materialize in real world usage. This is likely because of safety factors built into the ECM preventing the engine from running enough timing advance to take advantage of the octane of a blended fuel.

[bluGill]

The total amount you can get from changing the timing isn't very much. Even if you put in a whole new camshaft. Not to mention timing effects emissions as well.

The more typical way to do this is have a turbocharger (supercharger... I can never remember the difference and which you want when). You and run more boost which increases the compression ratio. However this requires an expensive turbo and so isn't a popular option.

I'm not sure why turbo cars have not made these modifications though. There are probably other trade offs I'm not aware of.

[jgust]

Exactly. More ICE cars are coming standard with turbochargers which would enable more to take advantage of the extra octane, but it's an optimization problem with constraints: fuel efficiency, reliability, drive-ability, emissions to name a few.