a model where new people have to be invited/referred by an existing well-established Steemian.

In my opinion, it's not feasible. Many people hear about it from social media where Steemians are doing promotions.

Secondly, what's the definition of a well-established user? Reputation 65+? What if once achieving that they start account farming?

Scammers will always be there. If we can't stop their breeding, we can certainly control their growth.

Ensuring that the big Steemit curators (sc01,02, 03...) don't give their votes to the fake accounts.

This is one way. The criteria can ofcourse be decided. It should be more than vanity metrics.

That is bad for newcomers - but they would need to build up their support base by engaging with the wider community. The wider community en masse would then do the filtering of who is fake and who isn't.

That's how it should be in any community. The wider community should decide.

For this, the team will have to re-think all their initiatives because the scammers will then be after booming support and community curators. We cannot control an individual's opinion about a user but booming and all steemcurator accounts need to be in trust worthy hands.

The idea of having "anonymous but most trusted" team of community curators has previously been floated around.

This would take much longer (as in old Steem) to build the Reputation to the required threshold for sc0x votes.

The kind of people we actually need on Steem will stick through this slow start.

1. AI Steem

I'm cringing even at the thought of this phase.

I'm not against AI but unfortunately, it's the biggest threat to the community of creatives in the whole world.