I've been running 91AKI pump gas in my UL350iS engine on my RV-12 for years. Here in California that means "up to 15%" ethanol. Each time I've tested the fuel I get from my local station, it's been in the 8-12% range.
The UL engine is an air-cooled flat four and is similar to an O-200, but with an EFII and 8.7:1 compression. At about 100 hours, I replaced the cylinders (off topic, but it was due to excess oil leaks that UL mitigated with an upgraded cylinder base design); I took the opportunity to install 9:1 pistons at that time. With over 500 hours on the engine, it still looks new via borescope inspection and compressions are 78-79 over 80.
I have tested my 540-X on an engine stand using 91AKI with 15% ethanol as well (discussed at length in the Traditional Engine forum) at 9:1 CR. The summary is it ran well and I plan to run on the same pump gas when I start flying it. I also have an SDS EFII and am able to control ignition advance for intake air and engine conditions, which is a great tool to mitigate margin to detonation (which is the general concern for running lower octane fuel; with its higher octane number, ethanol increases the margin to detonation).
As mentioned, with fuel injection running at higher pressure (45psi vs ~5-7psi carburetored), and constant cooling return flow (~250-300% return flow), the issue of vapor locking is effectively eliminated.
To your concern over the effects of ethanol on the engine itself, using Viton seals resolves nearly all of the issues. The only other real concern is production of aluminum triethoxide, Al(OC2H5)3 - however that concern is generally very over stated. It requires the presence of water to form and is a very slow reaction, taking very long time to occur. For example, I use an aluminum tank in the bed of my truck to haul fuel to the airport. That tank has been in use since 2018 with fuel in it continuously; standing most of the time. I drained the tank to inspect it this last September and found there is zero presence of aluminum corrosion in the tank (which is evidenced by a white, somewhat slimy, corrosion layer. The tank still looks very new.
If you were going to leave your aircraft in storage for longer than 3-6 months, then I would recommend draining (or consuming) the ethanol containing fuel from your tanks, but otherwise "fahgetaboutit".
I no longer have my RV-12, but before it left me, I inspected my fuel tank with a borescope and it looked pristine.