This is interesting stuff, and I think that the shift from taking Moorean facts, as it were, one at a time, to looking at “Moorean situations,” may very well be an extremely fruitful one. (In particular, I think it may help a great deal in thinking about the twist on Moore that you get in On Certainty.) But I’m a bit puzzled by the way you try to motivate backing off from Moorean situations to the (intentionally) epistemically much weaker “quasi-Moorean situations.” It seems that you are trying to do this motivational work at the beginning, when you say:

‘A Moorean fact, roughly, is any proposition of which I am more certain than the premises of any argument to the contrary (I ignore for simplicty the implicit category error). So construed, I suppose I don’t believe that there are any Moorean facts; there just are no individual propositions (or at least very, very few) that I am willing to hold onto “come what may”.’

Now, as Moore himself might say, so far as this is intended as an arbitrary verbal definition of the phrase “Moorean fact,” I have no quarrel with it. But if you are intending to provide an interpretation of Moore, I think you’ve got something importantly wrong; and it seems to me that what you’ve gotten wrong is important, since it points to a possibility that you seem to have neglected in this post.

Specifically, Moore does not hold that deliverances of Common Sense — such as “Here is one hand,” “I ate my breakfast before I ate my lunch,” “there are many other people like myself who know that they have hands and that they ate their breakfast before they ate their lunch,” et cetera — are irrefutable, or that we must hold on to them “come what may.” On the contrary, he is quite clear (see, for example, “What Is Philosophy?” in Some Main Problems of Philosophy) that Common Sense propositions can be, and have in the past actually been, refuted by careful empirical investigation (exploration in a literal sense, astronomy, physics, etc.). But empirical investigation and philosophical analysis are notoriously not the same thing; and what Moore does argue is that “Moorean propositions” are more certain than any purely philosophical that might contradict them. The idea here is not that there can’t ever be reasons to (say) decide that you don’t have a hand in front of your face after all; it’s that the reasons you have had better be better than your “metaphysical intuitions.” (For some provocative discussion on this and related points, see Bill Lycan’s Moore Against the New Skeptics.)

But if we take “Moorean situations” to mean what Moore means by it, rather than the way that you glossed it here — that is, not as stuff we oughtn’t ever abandon on any grounds, but rather stuff we oughn’t abandon on purely philosophical grounds — then I’m much less clear on why I should want to retreat from full-blown Moorean situations to “quasi-Moorean” situations as an epistemic tool. Why not hold out for all the constituent propositions in the situation rather than a good many, when all that you have to stare down to stick to all of them is a bunch of “metaphysical intuitions”? I think there are many situations that I’d be willing to trash any purely philosophical premises in order to hold on to; for example, exactly the situations that Moore describes in “Proof of an External World,” “The Defence of Common Sense,” “Four Types of Scepticism,” etc.