I surely hope Valve is working on Half-Life: Episode 3 and Portal 2 using both the current (and continuously improved) DX9c engine and a brand new DX11 engine.
DX11 is over a year old now, and Dirt2, which came out almost immediately after DX11 already incorporated a few DX11 features. Sure, not enough features, but it's been a year now, and after that initial experimentation time it is time to gradually move on to DX11.
On the consumer software side, most people are ready or will be in the coming months - Windows Vista began shipping in early 2007, so by the beginning of next year it will be 4 years since, and Vista also supports DX11.
On the hardware side it's a bit more complicated; there are many more cards that support DX10 right now, but given that DX11 is easier and, well, it's here, there is no sense in going for that anymore, especially as ATI is already coming out with a second generation DX11 hardware. Nvidia will also probably respond with something in the next few months, so it's really time to push the quality where we, PC users, deserve it to be.
And if there is one company capable of defying the console system, it's Valve. They have a history of making a great, scalable engine, and they were the first, in 2003/2004 to release DX9 in all it's glory with Half-Life 2, when there was still only one generation of DX9 cards (in 2003; two generations in 2004).
It's about time to start moving away from console-like graphics; we're the Formula 1 of games, we can't be pushed back anymore!