This is really important for me especially as I am borderline Vitamin D deficient and K2 nearly gave me a heart attack.
I will say, there may be some connection to vitamin D levels in terms of how one reacts. I had lowish levels (30) and they went even lower (20) after a week or two of K2, so it seems to sort of "burn" the vitamin D or increase the need for it. This could potentially be harmful for those who are already on the low end, though I'm not sure that's the only reason to be worried about K2. I would guess that the proper ratio would depend on how high your D levels are in the first place.
Personally, I doubt I will ever take K2 again regardless, which is depressing since it seemed to have a lot of good effects. But the side effects are just too scary.