But can you mix 100LL with 96UL and it still run ok ? So if you haven't got accesses to 96UL all the time you can revert back to 100 LL if you need to.
The two are obviously mixable because 96UL is avgas 100LL but without TEL.
So you will get an octane rating somewhere between the two.
This one hangs on the engine's detonation margin. I think the manufacturers are realising that actually it is much harder to get most engines to detonate than anybody had previously thought, so 96UL has potential to replace 100LL in perhaps all engines, with the real issue being whether anybody is going to do the tests and approve it.
Regards alcohol, I note that Socata allow up to 2% IPA in avgas, as fuel icing protection. I know nothing about this but would have thought that since IPA is alcohol, it has a similar fuel system eating potential to ethanol, and if IPA is approved at 2% then that particular fuel system is probably OK.
A lot of fuel tanks are sealed with
PR-1422 and that appears to be alcohol resistant, but that would be the hardest thing to change; the seals in the pipework can be changed easily, in most cases. But on a CofA plane you need to be following an approved process of some sort.