I wouldn't buy one because of all the emission system fail built into them (2009 through 2014). The thought of possibly spending more on emission system failures than a car is worth is just absurd.
If emission system maintenance costs are many times more than the savings you would get from the VG fuel economy a TDI can deliver the financial benefit just isn't there.
There are people that will say oh ya? my 2010 or whatever has been just fine. Not much consolation to folks that have to spend most of the buy back money amount on repairs so they can get the buy back.
I would wait for at least the 2018 A7's and see what kind of repair cost history the A7's rack up before buying.
As an aside, I would take a close look at the Mazda SKYACTIV-D. Their claim is that they can control NOx emissions without the Rube Goldberg after treatment for NOx that VW and other manufacturers are currently using. They claim that SKYACTIV-D controls NOx during the combustion process not after it.
They plan on selling them here and if SkyActive-D pans out, that is were my money will be spent.
https://www.linkedin.com/pulse/how-mazdas-skyactiv-d-technology-works-masoom-kumar