For those well versed in the French language, a final report......
https://www.bea.aero/uploads/tx_elyd...1_addendum.pdf
The next post is Google Translate with no attempt by me for any corrections or read through prior to posting.
However, the BEA site did have a single paragraph summary in English.....
"The pilot stated that he had perhaps braked involuntarily during the takeoff roll, by using the rudder pedal at a time when he was increasing power. The aeroplane tilted forward onto its nose and then flipped over onto its back"
Perhaps it is one of those types where it is difficult to input rudder pedal without applying some brake(or one has to ensure that feet are properly positioned to ensure this doesn't happen).