Good point but I was thinking of the lens mount and chassis - are these strong/rigid enough? For example, when using my 7D2 and large lenses I am careful to grab the lens not the camera when I lift it. With my 1DX I just grab the nearest bit I can get hold of, swing it up and shoot - this is normally the landscape grip.
A little while back I did look into the A7 series as I thought the A7R2 as it makes a great landscape camera - well it certainly does! My two concerns were that I would have to use adapted lenses, just fine for landscape but not very good as a wildlife backup. Also the camera did not feel like it was designed to cope with heavy lenses and published internal diagrams seemed to support this. Of course I could be completely wrong but would I take the chance when this is likely to be on the front?
http://www.wexphotographic.com/canon-ef-800mm-f56-l-is-usm-lens-1024502/
To me the A7R2 was simply an excellent camera that did everything I wanted - but only for one aspect of my photography. This is in no way denigrating the camera, it is just not designed with me in mind. The A9 is being touted as a high speed action camera, perhaps it is, but we won't find out until we have high speed (response) lenses of suitable focal lengths to find out. I hope they will come because Sony are shaking up the market and the more they do that then the more users of all brands will benefit!