Oh as developers you better just get used to supporting DirectX 11, because a lot of people still don't want to be brute forced into these situations.
The thing is, the majority of gamers will update based on the available cash, and so gamedevs will be targeting the expected hw base at the time of release.
So it really depends, whether you except the gamers to go on spending spree (nvidia and intel would certainly love that), or not.
A huge portion of the gaming market (China and large parts of Asia) is still using Windows XP. D3D9 renderers aren't going anywhere.