I guess the two alternatives that seem salient to me are (i) something like HMV combined with pairing individuals via cross-world identity, or (ii) something like HMV combined with pairing individuals who currently exist (at the time of the act) via cross-world identity, and not pairing individuals who don’t currently exist. (I take it (ii) is the kind of view you had in mind.)
If we adopt (ii), then we can say that all of W1-W3 are permissible in the above case (since all of the individuals in question don’t currently exist, and so don’t get paired with anyone). But this kind of person-affecting view has some other consequences that might make one squeamish. For example, suppose you have a choice between three options:
Option 1: Don’t have a child.
Option 2: Have a child, and give them a great life.
Option 3: Have a child, and give them a life barely worth living.
(Suppose, somewhat unrealistically, that our choice won’t bear on anyone else’s well-being.)
According to (ii), all three options are permissible. That entails that option 3 is permissible — it’s permissible to have a child and give them a life barely worth living, even though you could have (at no cost to yourself or anyone else) given that very same person a great life. YMMV, but I find that hard to square with person-affecting intuitions!
This is helpful.
For what it’s worth I find the upshot of (ii) hard to square with my (likely internally inconsistent) moral intuitions generally, but easy to square with the person-affecting corners of them, which is I guess to say that insofar as I’m a person-affector I’m a non-identity-embracer.