Here's how Bostrom put the old SIA:

Given the fact that you exist, you should (other things equal) favor hypotheses according to which many observers exist over hypotheses on which few observers exist.

That's similar to claiming that the majority of observers exist in observer-rich worlds - which seems fairly plausible.

In multiverses or many worlds, SSA and (new) SIA are the same thing.

It turns it into a non-issue for me. Maybe the focus of attention should switch to obersvers vs observer moments.