Brian
The use of the take-over push button is now a well established SOP. Some historical incidents which have made this so, include an occassion in Sydney in the early 90's when there was a RWY infringement. The Capt initiated a GA and took over from the FO on short finals. However, the F/O still had stick input and GA performance was compromised.
Having the Side Sticks algebraically summed presents other problems in what you refer to as the man-machine interface.
For example, if you overspeed the aircraft, there is a 1.75G pull-up. Problem being, the pilots possibly panicked input is added to this aswell!Two pilots panicked inputs, now summed together, and you run quickly up to the aircraft's 2.5G limit in an overspeed scenario.
I see the report makes mention of what can be described as speed tape confusion. An anecdotal problem with Airbus PFD's.
Secondly, there was no mention that I can find, if the aircraft was software upgraded to have the automatic reinstatement of FD's on GA.