This includes viewport and scissor rect (core in 1.0), and depth/stencil state (comprised entirely of elements in EXT_extended_dynamic_state).
Further patches add other dynamic state extensions and make other parts of the pipeline state dynamic.
Theoretically dynamic state should be an improvement, giving greater freedom to the driver and hardware to optimize, and (perhaps more importantly) reducing the time needed to look up and compile new pipeline states. In practice I haven't observed a clear and measureable difference in either performance or stutter; however, my testing has been extremely scarce.
Note: This patch series in particular introduces a new validation warning which prints on almost every draw. The warning is described at [1]. Similar warnings are triggered by future patches making other parts of the pipeline state dynamic.
An unfortunately internal Khronos discussion has determined that the warning is undesirable, and there is currently motion to adjust the specification accordingly; however, the validation layers have not yet been adjusted.