I don’t know much about nematodes, mites or springtails in particular, but I agree that, when thinking about animal welfare interventions, one should be accounting for effects on wild animals.
(As Vasco says, these effects plausibly reverse the sign of factory farming—especially cattle farming—from negative to positive. I’m personally quite puzzled as to why this isn’t a more prominent conversation/consideration amongst the animal welfare community. (Aside from Vasco’s recent work, has ~any progress been made in the decade since Shulman and Tomasik first talked about the problem? If not, why not? Am I missing something?))
There’s an old (2006) Bostrom paper on ~this topic, as well as Yudkowsky’s ‘Anthropic Trilemma’ (2009) and Wei Dai’s ‘Moral Status of Independent Identical Copies’ (2009). Perhaps you’re remembering one of them?
(Bostrom disagrees with the second paragraph you cite, as far as I can tell. He writes: ‘If a brain is duplicated so that there are two brains in identical states, are there then two numerically distinct phenomenal experiences or only one? There are two, I argue.’)