A Thought Experiment against Humean Supervenience: Conceivability & Intuitions

One thought experiment that objectors against Humean Supervenience are quick to suggest is that of two possible worlds which both contain only one existing material object that always moves in a constant velocity. The thought experiment goes: in the first world, the particle is governed by the law that all particles move with constant velocity and in the second world, the particle is governed by the law that all particles obey Newton's Second Law; in other words, in the second (and not the first) world, if another particle had existed there, they may have had an effect on one another's velocity.

Is this a good counterexample via thought experiment? In a recent paper, Ned Hall tries to construe this counter-example as relying on the 'Conceivability entails Possibility' principle. And he therefore dismisses it. It is certainly true that the set-up of the thought experiment involves the (C-->P) principle, insofar as it must be committed to it being possible that there could be a world with only one particle and a world differing from another in only its modal facts.

But although I whole-heartedly dismiss the (C-->P) principle, I'm not so sure that a counterexample wherein two different objects in two distinct possible worlds are intrinsic duplicates and yet differ in their nomic-profiles is to endorse a possibility only on the basis of conceivability. Why is this such a leap in conceivability? I think the non-reductionist example is meant to (or at least, should aim to) exploit a seperate intuition; not the C-->P intuition. The intuition is: how a particular object (or kind of event) has been, is, or will be says nothing about ways it might have been.

It won't do to simply dismiss the non-reductionist thought experiment on the basis that it assumes that one world could differ in its laws while another one does not. For while this is assumed, and while it is an assumption that tips the scales, so to speak, it is not an altogether unwarranted assumption. And the onus is on the Humean to explicate the ways in which this thought example goes wrong. It won't be enough for the Humean to claim that the two worlds differing in their Laws is just impossible, any more than it will do for the non-reductionist to claim that it is possible. The non-reductionist position exploits an intuition, one that, for all I can tell, is fairly plausible, while the Humean position combats this intuition, but with no reason other than the fact that it does not accord with his theory.