I agree there are valid concerns. The biggest concern, IMO, is with cars made during the late 1960s through early 1980s, that have fixed main jets in the carbs and hence cannot easily be adjusted to the richer mixture required to properly burn E15 (or E85 for that matter). Those engines were already tuned to the edge of lean misfire (to reduce emissions) so burning E15 will push them over the edge (under at least some conditions) leading to unburned or still-burning fuel being dumped into the exhaust causing both a huge increase in emissions and potentially severe engine damage. I don't have the link handy, but there were even some EPA (or perhaps it was CARB) studies that showed that "oxygenated" fuel would cause a net increase in pollution because of that effect, even though there are (were) relatively few cars left on the road from that era.
However, unless you have a TR250 or early TR6 with the fixed jets & needles, your TR can easily be tuned to run properly on E15. And IMO E15 isn't going to "eat the fuel system" any more than E10 already has. By now, anyone living in CA has already made the changes required to tolerate ethanol (which include changing all the soft fuel lines and fuel pump diaphragm). Likely most of the rest of the US has as well, or at least will have by the time you can only buy E15.
My opinion, our efforts are better spent adapting to the future, rather than trying to prevent it.