he desire to fit in, to be respected, liked and admired by other people, is one of the core desires that most (virtually all?) people have. It's approximately on the same level as e.g. the desire to avoid pain.

I think the comparison to pain is correct in the sense that some part of the brain (brainstem) is responding to bodily signals in the same mechanistic way as it is to pain signals. The desire to fit in is grounded in something. Steven Byrnes suggests a mechanism in Neuroscience of human social instincts: a sketch. 

We call it  "peer pressure" when it is constraining the individual (or at least some of them) without providing perceived mutual value. It is the same mechanism that leads to people collaborating for the common good. The interesting question is which forces or which environments lead to a negative sum game.

some people would just develop a different persona for each group

That is possible but maybe only more likely if the groups are very clearly separate, such as when you are in a faraway country for a long time. But if you are e.g. in a multi-cultural city where there are many maybe even overlapping groups or where you can't easily tell which group it is, it is more difficult to "overfit" and easier to learn a more general strategy. I think universal morality is something of the more general case of this.

I would be interested in what the questions of the uncertain imitator would look like in these cases.

Never saw "SUVAT" before. Might be a term known specifically in the US?

I think this approach can be combined with self-other overlap fine-tuning (SOO FT, see Self-Other Overlap: A Neglected Approach to AI AlignmentI'm part of the SOO team, now an ICLR submission). The difficult part of SOO is to precisely isolate the representation of self and other, and I think it should be possible to use ERA to get a tighter bound on it. Note: I'm part of the SOO team.

I'm not clear about what research by Michael Levin you mean. I found him mentioned here: «Boundaries», Part 3b: Alignment problems in terms of boundaries but his research seems to be about cellular computation, not related to alignment.

Cannell has also talked about "empowerment of other"

Do you mean this? Empowerment is (almost) All We Need

folks who have been discussing boundaries ... zone of agency

and this: Agent membranes/boundaries and formalizing “safety”

I recently heard the claim that successful leaders make themselves easy to predict or model for other people. This was stated in comparison to successful makers and researchers who need to predict or model something outside of themselves.

It depends not only on the age/maturity of the child but also on the country/area. 

Here, in Hamburg, Germany, it is common for groups of fourth-grade students (age 9-10) to use the public transportation system and complete some tasks (go to some station and find a memorial, etc., competing who finishes first) and this was the case before mobile phones. I did this too at that age.