So, I busted out the 1 Coupe manual and there's no mention of fuel additives voiding warranty. Interestingly, there's additional language cautioning that using fuel with more than 10% ethanol will not void your warranty with respect to workmanship or material defects. However, the use of e85 will damage the motor and void warranty. Sort of conficting.
Just for reference, I checked the 5 series manual for the new f10. The language is similar with a few distinctions. For instance, the maximum amount of ethanol used cannot exceed 10%. The manual doesn't explicitly state that using higher than a 10% blend will void your warranty, only that unscheduled "maintenance" will be required. I assume they mean you that have to pay for this maintenance.
Here's an article from a couple years back which claims that ethanol blends damage motors and more specifically, fuel delivery systems.
http://www.businessweek.com/lifestyl...514_058678.htm
So, I wonder if a little MMO would be good for these motors? Seems like it could be.