you would support impregnating every fertile female, voluntarily or forcibly, if you expect this to maximize QALY

No, but that's not what the repugnant conclusion is. The RC is about the desirability of an end-state - highly populous worlds could be very desirable and yet some methods for achieving such worlds still be morally impermissible. There can be side-constraints, to use Nozick's (?) terminology, or other values at stake.

You might find [this article] on population ethics interesting.

Or do you qualify it by saying "maximize the QALYs of everyone who is already alive"?

I think there are many plausible approaches, including a consequentialism-of-rights. I included "maximize the QALYs of everyone who is already alive" because I wanted to show that the argument applied to many different systems, but I do not actually think that system is very plausible.

Then you are back to the definition of when to count fetus as alive,

I agree that many arguments can ultimately be reduced to arguments about the moral status of fetuses - in fact I say so in the OP!

and this is again a Schelling point argument, EA or no EA.

But here I must disagree. It seems plausible that there is actually a fact of the matter whether one has moral value / how much value one has. I don't think this is particularly controversial, except I guess to some anti-realists.