Great post. There's one part (two if you include Manfred's critique) that I don't buy, and seems to go beyond what you need for your core points:

Arguing which is "correct" is pointless. Both will possess all the features of selfishness we've used in everyday scenarios to define the term. We've enlarged the domain of possible scenarios beyond the usual set, so our concepts, forged in the usual set, can extend in multiple ways.

The various approaches to identity agree on the undisputed everyday scenarios, but that doesn't mean they're all equally natural and elegant extensions of our concepts. Compare two early humans who have agreed that sparrows, crows, and pigeons are all "birds". Then they encounter a penguin. It doesn't fly! Argument ensues! That doesn't mean that there isn't a unique best answer to whether this new thing is a bird. Maybe there is, maybe there isn't - agreement on paradigm cases plus disagreement about others doesn't predict much.

Precisely because value questions are getting entangled with semantic questions, the semantic personal identity question is made harder than it needs to be. I think psychological theories of identity are only made plausible by building-in the assumption that whatever identity turns out to be, it must always turn on facts that most people would instantly recognize as valuable. But that's getting off topic.