What is the mechanism for cylinder damage from ethanol? It's not good enough to say ethanol damages engines - how does it do that? Wear on engine internals is indeed cumulative, but even ethanol free fuel has zero lubricating capabilities - that's the job of the mix oil.
Phase separation in and of itself is not going to score a piston because it results in free water, which cannot be vaporized in a carburetor - therefore your engine will not run, or it will run so obviously poorly that you will know to shut it off and find out what the problem is. If you try to keep it running under those conditions you'll likely kill it. On the other hand I've had water in fuel long before ethanol, and it didn't vaporize then either. So yes, ethanol is hygroscopic and that's problematic if your fuel is exposed to water. But the amount of ethanol does not effect the amount of lubricant in the mix, so engine damage would still only be a consequence of running lean.
If the ethanol content varies enough to effect the tuning to the lean side then the operator should hear that and adjust the mixture - given the really crude carbs on these engines (i.e. without M-tronic or Autotune) YOU are the feedback system. As we discussed recently most of these things are so cheap and crude they usually don't even have properly placed bowl vents and so even a bit of typical filter clogging will change the mixture (rich, fortunately). There are no high speed or high load enrichment systems, usually no accelerator pumps, just a high and low speed fixed jet and a couple of transfer holes. I'm always suspicious of every new tank of fuel, but I store them properly so once I've confirmed the tuning on a new can I know what to expect from it.
If the amount of ethanol in the fuel is changing at the station, then it's doing that for every automobile engine filling up there. Why doesn't it matter (and we're talking coated aluminum cylinder bores on many recent engines)? Because the cylinder walls are still lubed, the mixture is controlled, and if it is injected any water droplets will be pumped through resulting only in a misfire. For this reason I think M-tronic or Autotune are a good idea for many operators. I tend to like things simple, but I'm willing to accept the compromises and know I must keep the mixture adjusted.
Having said all that I think ethanol in fuel is a terrible idea, but more because it takes more energy from oil to make the ethanol than you get back, and because I think burning food is dumb.