With ATI (<M>, +kms) and Intel i915 (<M>, +kms) I manage to boot into console, but ONLY if I blacklist the Intel 
drivers. If I probe the intel driver *WITH* modeset at *ANY* time (on boot by not blacklisting them or later), my screen 
turns black.

Besides, on dmesg I get confirmation, that

VGA switcheroo: detected switching method \_.SB_.PCI0.GFX0.ATPX handle

but I do not get a vgaswitcheroo interface in debugfs of the kernel.

I attached dmesg, so maybe someone spots something.