As I understand it, xserver-xorg-video-modesetting should be used
instead of xserver-xorg-video-intel, for chips supported by the i915
kernel driver. So the latter should be changed to limit the device IDs
it claims, then both of them should be backported.
Currently 4.6.0 doesn't work with skylake for me when I plug in a
3440x1440 monitor on a Dell XPS 9550, both with and without xserver-
xorg-video-intel installed. It never has worked reliably on any kernel
version. Currently, the monitor works maybe 20% of the time - so if
you persist for 5 boots you've got a reasonable chance of getting
lucky. The only noticeable change from 4.5 to 4.6 is in the kernel
backtraces produced - they have got fewer, and they are only warnings
now.