As of this afternoon, Kenneth Graunke's work for implementing GL_ARB_tessellation_shader support for Ivy Bridge and Haswell is now within Mesa Git master. This makes tessellation support implemented for all hardware capable of doing so -- Sandy Bridge and older are not.
Thus this crucial GL4.0 feature is now crossed off the list and the Intel driver remains on the verge of GL 4.0 compliance and soon after that OpenGL 4.2 for supported hardware generations.
This latest Intel GL4 work will be found in the next Mesa release due out around March. Hopefully by then GL 4.2 will be reached since the Intel Windows driver for a while now has already been exposing OpenGL 4.4.