Well the Inquirer tells us that DX10 will support shadermodels even over 4.0, also the DX10 should be faster, with many new goodies, like a completely new (?) Geometry Shader model.
But what I'm really worried is this:
"As of DirectX 10, to be introduced in Windows Vista, 3D features will be bound to version numbers of Direct3D. What this means is that all 3D vendors will support the same features, guaranteeing compatibility across the board. Although this may sound great, allowing for a more standardised games development environment, the reality is that Microsoft will soon be regulating the introduction of 3D features, leaving companies such as NVIDIA and ATI at the mercy of the software giant."