Here are some facts, in an interview before the accident the pilot said they had removed ten feet from the wing span and had done some other mods to get up to "jet" speed, around 500 mph, he said he thought the "systems" could handle the stress but they weren't postive. I saw a video of the interview. The elevator trim tab did separate in flight, there is one video where you can see it come off. In another video you can see the plane go into a tight violent verticle loop right after the trim tab leaves and go into the ground. Those are the facts that I have seen in videos.
My opinion is that when the trim tab came off the plane pitched up violently and went up, over and into the ground, I think the pilot was then unconsious or pinned forward and unable to control the plane. It could be a while before the NTSB releases a finding.
It is sad. In the United States much is done to make airshows safe, but bad things still can happen.