Well, to be honest fuel quality has improved significantly over the last couple of years. HOBC on ktuner/hondata basemaps works very well now. But when it comes to flex fuel kits, they only analyze ethanol. Without a custom tune there is no benefit to running E20/30/40 or whatever ratio of ethanol blend because the Ecu simply wouldn't know what to do with the ethanol content. This is why a custom tune is required to advance the ignition timing and boost etc based on ethanol content.
On a side not. Ktuner still doesn't support automatically raising boost and ignition timings based on ethanol on PKDM ecus. The tuner has to manually set the boost in the main tables. USDM and most other Ecus adjust these parameters automatically by analyzing ethanol content.