There's no such thing as an "FS9 version" of our products, the license is valid for both FS9 and FSX, which means you can purchase now and install into FS9, and then simply download the FSX version and install it into FSX without having to purchase it again.
This means, there's are reasons to do an "FS9 end-of-life" sale, because we never had FS9-only products, not as FSDT at least. We might do it for Cloud9 products, since most of them are FS9-only but, it's a decision that Cloud9 owners need to agree on first.