Whilst engaging in general speculation is never helpful (and the endless debate about the FR24 data is a fine example of the bottomless rabbit holes some people like to go down) the emerging pictures and information on the wreckage spread tend to suggest a high altitude break up. Caused by I've no idea.
The picture of the tail section shown on various news media sources is interesting though. Obviously the collapse damage to the empennage is mostly down the impact with ground. Likewise the lower fuselage damage and that around the L4 door. There are, however, signs of the fuselage skin peeling outwards (red arrows) possibly indicative of a force acting outwards from within. Similarly there's the very clean break around the fuselage frame. It looks like an initial failure as opposed to something twisting and tearing apart as it fell.
