Buy A6 now and you'll get an upgrade to the same edition for A7 without any additional payment.

Example:
Buy "A6 Commercial" now and when A7 is released you'll get a download link (I guess) where you can download the A7 setup file.
Then you can use your A6 key file to activate your A7.

But: Its still only ONE licence!
So you cannot resell your A6 and still use the A7 because then two people would use the same key file.

EDIT:
@Aliakey: People who have purchased A6 since the 29th Jan 2007 will get the A7 for free as far as I know.
This means: buy now!