While most hardware with kernel mode-setting support already has a matching X.Org driver that is KMS compliant or even still provides user-space mode-setting, this driver would be a simple, un-accelerated fall-back driver. It's similar to the VESA driver, but uses Linux KMS.
The features of the xf86-video-modesetting "restart" driver branch include ARGB cursor support, RandR 1.2 support, and dirty tracking ioctl support. What's changed from the original -modesetting work is that it drops all DRI2/EXA knowledge, uses the kernel dumb interface directly for buffer object creation and mapping, the mode-setting logic is derived from the Radeon driver, and probing is based upon the fbdev driver.
You can see David's email to dri-devel about this recent driver work.
While this driver is meant to be universal for hardware that has proper KMS support, there isn't any hardware acceleration. If you're looking for a universal X.Org driver with acceleration, and don't want to use the driver specifically targeted for your hardware, there is the Xorg state tracker (and now the XA state tracker too) for Gallium3D that relies upon KMS and then offers shader-based EXA/X-Video acceleration. There's also the recently announced Glamor work, which does have a generic driver for KMS environments while depending upon Mesa/EGL.