clone

randr + client:
git://people.freedesktop.org/~airlied/randrproto prime
git://people.freedesktop.org/~airlied/libXrandr prime
git://people.freedesktop.org/~airlied/xrandr prime

dri2proto:
git://people.freedesktop.org/~airlied/dri2proto prime

libdrm:
git://people.freedesktop.org/~airlied/drm prime

mesa:
git://people.freedesktop.org/~airlied/mesa prime
(simple patch should probably just pick onto master)

xserver:
git://people.freedesktop.org/~airlied/xserver prime-101

drivers:
git://people.freedesktop.org/~airlied/xf86-video-nouveau prime
git://people.freedesktop.org/~airlied/xf86-video-intel prime

Clone + build + install everything somewhere:

run X, it should pick up intel + nouveau in the logs,
run xrandr --listproviders
output is crappy, should show 2 providers,
Providers: number : 2 0
Provider 0: 173 0 0 0 0 0
Provider 1: 70 0 3 2 0 0

Find the provider with 3,2 in it, then
xrandr --setproviderrole 70 2

then with all LD_LIBRARY_PATH etc setup to point at mesa,
make sure perms are correect on /dev/dri/card*
run a wm/cm

glxinfo - should give Intel
DRI_PRIME=true glxinfo should give nvidia

DRI_PRIME=true openarena should maybe work