You could say that that 3rd way IS part of the physicalist picture already I think. As you say, there are such gaps in our understanding at this point we cannot say we've probed the depths of our brains and still found nothing.
It is like searching the ocean for something that by all accounts should be in the ocean, and deciding that perhaps the thing cannot be found, despite having large portions of the ocean still to search. It is too early to make that claim.
I'm not saying that there are not smug philosophers or scientists or just internet nerds that will declare the problem solved, clearly it is all in the brain and there is nothing magical to it but I think they would be incorrect. Modern physics is incredibly esoteric and shares more with meta-physics than what we tend to observe (which classical physics can explain satisfactorily for the most part). I don't think being physicalist is any impediment to having spirituality and and a sense of wonder about the universe and our place in it - the main difference to me is that we can't just accept a deus ex machina and call it a day. That may sound condescending but it isn't a choice for me personally.
It is like searching the ocean for something that by all accounts should be in the ocean, and deciding that perhaps the thing cannot be found, despite having large portions of the ocean still to search. It is too early to make that claim.
I'm not saying that there are not smug philosophers or scientists or just internet nerds that will declare the problem solved, clearly it is all in the brain and there is nothing magical to it but I think they would be incorrect. Modern physics is incredibly esoteric and shares more with meta-physics than what we tend to observe (which classical physics can explain satisfactorily for the most part). I don't think being physicalist is any impediment to having spirituality and and a sense of wonder about the universe and our place in it - the main difference to me is that we can't just accept a deus ex machina and call it a day. That may sound condescending but it isn't a choice for me personally.