David Airlie officially released the first version of the xf86-video-modesetting DDX driver this week. The xf86-video-modesetting driver is a generic KMS X.Org driver that will work with any kernel mode-setting DRM driver in Linux, but only provides shadow frame-buffer support.
The xf86-video-modesetting DDX driver is just for serving as an X.Org driver that's generic to work with any underlying KMS kernel driver in a generic way. It can be used in cases where there may be a KMS driver available but no DDX driver or in cases like USB-based video displays or dumb-frame-buffers where having an accelerated X.Org driver is to little advantage.
With this being a generic driver, there isn't any hardware acceleration support but all of the X.Org acceleration is being done using ShadowFB.
The release announcement of xf86-video-modesetting 0.1.0 can be found on the mailing list