Could psi have a materialist explanation?

This. ^^^ 

I was under the impression that "isms" like "physicalism" propose that even those things which intuitively don't seem to be physical will be found to be physical (or to supervene on the physical) upon more detailed investigation, not that the definition of "physical" will change with the wind. 

On the other hand, our intuitions about what we regard as physical can be expected to change with the wind, given that we have already discovered that they are woefully misbegotten. Solid matter is almost entirely empty space, for example. And, as Steve pointed out, empty space turns out to be physical, with some decidedly weird properties. 

When we talk about new findings getting folded into an "ism", it seems to be more about updating our perceptions than updating the "ism". But even so, what's wrong with updating models of reality? I don't understand the complaints - first the complaint is that science is unbending and dogmatic, and then the complaint is that it is too willing to change?

Linda

I think most likely the point is that suggesting that things will ultimately "turn out to be physical" (whatever that means) doesn't really tell us anything. Something that we on this forum and our modern scientific and philosophical counterparts now might consider "physical" could be far narrower or more strict in scope than, say, 100 or many more years from now. 

So saying it'll all turn out to be physical or explicable in terms of "science" doesn't move the needle one way or the other really. It doesn't lend any credibility to either the proponent or skeptical side of things.