No, in that case you couldn't sell your A6 license without selling A7 as well. You'd simply be the owner of A6 and A7 and only pay for A6 - this is exactly what I have said.
Ok, here's another advantage: you buy A6 now and you don't have to worry about a potential price increase. I don't know if the price will increase or not, but if you buy now you can be sure that the potential price increase won't affect you.