Once I started using fuel stabilizers in the two stroke motorcycles and boat outboards full time the gunk went away, ethanol or not. I have doubled the dose now which is the same idea in the more concentrated "Stabil Marine". Pri-G works also and possibly SeaFoam.
Only nagging concerns I have are certain diaphragms. But I would be very surprised if the "up-to-E10" blends our state currently uses would be deleterious to the diaphragms, especially with part-time contact. No fiberglass fuel tanks or cork floats here to worry about.
I am going to cut out a short section of the oldest fuel line I have and leave it sitting in an ethanol blend all winter just to see what happens (I don't expect much). It is easy to verify you have an ethanol blend with a water absorption test.
If you don't take care of your 2 cycle, it won't last and most of the trouble I've had is carburetor varnish and fouled plugs. I can't think of any reason for a 2 cycle to burn a piston except low oil/fuel mix. The only way that happens is too lean or forgot to mix in the first place. A Lean 2 cycle runs REAL good, until it breaks. Adjust your needles until it runs the best and back off about a quarter.
I would be interested in straight ethanol fuel mixed with oil used in a 2 cycle. Maybe someone out there has done it in a racing bike or something? My bet would be it would run fine with the proper jetting and WOULDN'T FORM VARNISH IF NOT USED. My rum is quite old with no "floaties" and I have some 190 proof from decades ago in my stash that is clear as a bell. Try putting gasoline in a bottle for a year or two and see what happens.
The first thing I do with a dead mower or weedeater is smell the tank. I've taken he float bowl off a lawnmower before and the float was stuck like it had been sprayed with glue. I use a spray chemical to clean the stuff, but I think it might be freon based so I better not name it here. I think WD40 works to clean it( doesn't it do everything?) maybe even rubbing alcohol( I can't remember). Otherwise it's wire brush time and you can't get into those nooks and crannies with that. Also if you don't do a soak and wash, you may remove the float bowl later and still find "floaties" messin up the needle valve sticking. I just don't believe E10 make ANY difference. We don't have E85 where I live so I can't comment. Come to think of it we used E10 wayyy back in the '70s and ''80's before MTBE and I don't remember problems worse than usual then. I think we have had years of experience with E10 with no ill effect. StaBil works and I think I would use it in my 2 cycle can and outboard tanks even if I wasn't planning to leave it dormant for awhile. Sorta like insurance.
I can't speak for an inboard 4 cycle boat with a tank coated with plastic or Styrofoam floats. I think Styrofoam melts even with gas. Get a coffee cup and put some gas in it and report back. Maybe they are confusing styrofoam with cork or some other man made thing.
As a side note, ethanol does attract water is why they use it to REMOVE water from tanks, but most of the rust I've seen came from the vessel people use to FILL their tank or the gas station itself. If you have enough water in your tank to mess things up, it's most likely NOT from condensation unless you fill your tank in the rain.