In the cars that I've used straight E85 in, there's never been any residue of any sort. Quite the contrary, actually. Pulled out an in-tank fuel pump after 10k miles of going to full E85 on one particular car; the sock filter and pump pickup were spotless as if I just opened them up and hadn't installed them yet (this was in a track car with 298,000 on the chassis, fuel tank, and all fuel lines). Injectors were also perfect.
If you know all about E85, then you know the "gunk" it's said to leave behind is caused by the cleaning action of the ethanol dislodging fuel system deposits which thereby can cause issues.
Yes, iso alcohol would clean your fuel system the same as ethanol - and prevent the buildup of alkenes/olefins. You could use either one; indeed, I've heard of people using all sorts off different alcohols.
Virtually every vehicle built since the 1980's is "E85 compliant" in terms of corrosion resistance, and fuel tanks aren't made from steel anymore. When E85 was just catching on here, I used to post a material compatibility document from DuPont Labs, where they tested E85 with all sorts of rubbers and plastics and metals. Long story short, E85 is not harmful to any modern day materials in fuel systems.
The car I was talking about above was a 1994 Volvo 850, which was driven as a daily for 3 years on full E85, until 25psi wore it out. When I parted it out, all fuel system components were still spotless. I still have the injectors and fuel pump from that car to use in a future project.