Two papers on counterpart semantics
I've thought a bit about counterpart-theoretic semantics last year, both for natural language and for quantified modal logic. Here's a paper in which I present my preferred version of this framework as applied to natural language: Counterpart Theory and the Paradox of Occasional Identity. Apart from the semantics itself, my main claim is that the advantages of counterpart semantics do not require the metaphysics of "counterpart theory".
Here is another paper which covers related grounds, but from a more logical point of view: How Things are Elsewhere: Adventures in Counterpart Semantics. Comments on either paper are very welcome.