The factory fuel system wasn't designed for ethanol, so there could potentially be long-term side effects to the fuel injectors. That said, we haven't experienced any side effects from running mild ethanol blends in the last few years of doing these mods on hundreds of ATS-Vs with nearly identical fuel systems.
On higher ethanol blends, there is a very real risk of a fuel injector sticking open. We typically recommended preventing this by recommending that a tank of pump gas be run through the system periodically. There are also additives you can add to each fuel tank when running E85.
For ATS-Vs, customers need LPFP, fuel cam, HPFP internals, alcohol content sensor and wideband in order to
safely run ethanol fuel blends. However, the CT4-V Blackwings are much improved, and can safely run E30 or E45 with just a fuel cam. In fact, we remote tuned one last week on E45 and the data scans look very solid.
Tapout Fuel Cam - Tapout Tuning
You can even run E30 on a completely stock CT4-V Blackwing, as long as you don't crank up the boost too high. But we would recommend the fuel cam anyways, to help provide a little extra padding.