What's really strange is all those new 4 seaters are designed with
engine requiring 100LL, instead of 91/96.

It part of a big bore engine.

True, but IO-470J/K can run on 80/87. I'm sure they'll do fine on
SR-20 airframe. It also won't be very hard for TCM engineers to
reduce the compression ratio a bit and make IO-550 run on 91/96.

My point is the aircraft manufacturers are short sighted. Relying on
a fuel that's going to be increasingly more expensive than automotive
fuel doesn't do GA much good.