Sounds interesting and almost like it's designed to go with the Sony 70-200mm f2.8 lens. I got this lens recently and, while it is clearly a superb quality lens, it is still a little slow to focus on the A7R2 when compared with the canikon equivs. I would expect this will no longer be an issue with the A9.

A comment on the lack of Sony lenses. While canikon clearly have a lead with the range of lenses available, I would say that I now have 5 E-mount lenses and they are all superb lenses. They are
Zeiss loxia 21mm - This is the best wide angle lens I have ever used. It is tiny and fully manual, but that isn't much of a problem with this lens. Not cheap, but worth every penny.
Sony-Zeiss 50mm f1.4. I still have the Canon 50mm f1.2 which is a takes beautiful pictures, but the Sony-Zeiss lens takes even better pictures and it is much sharper. It is one of those lenses that you just wish you could use for everything. Again, not a cheap lens, nor is it small.
Sony 90mm G-OS f2.8 macro. Better than the Canon 100mm II macro - need I say more.
Sony 70-200mm f2.8. I haven't used this lens a lot yet and Have have never owned a Canon equiv, so I can't compare. But, it does take superb pictures.
Sony 24-240mm. This is used mainly for video, but is a great general purpose lens also. Canikon have no equivalent

While I would like a greater range of lenses, they are slowly arriving and the ones that Sony do release are really very, very good lenses. Those first 3 lenses I have listed are better than the anything that Canon produces (imo). The 70-200mm may be better, but I have nothing to compare it to. The 24-240 is unique.