I asked about it on ButtRider and I got this answer.
"BMW specify all models going back many many years are compatible with E10, that includes all year models of the 650GS, that means no issues with plastics, fuel lines, seals etc so dont pay any attention to any scare stories that may be floating around, they are just misinformation
I have been using Oz E10 RON 95 in my single spark Dakar for over 5 years but I have the BMSC programmed for RON95 which cant be done on the dual spark models as there is no firmware for RON95, the single spark RON91 did not like E10 RON91, it seemed to get grumpy round town.
I would expect the dual spark RON91 firmware to be a lot better than the single spark firmware so I would not expect any issues to arise."