Other thought: I think in recent years, AMAs have been trending towards decentralization towards the individual subreddit level anyways, because neat people want to interact with groups that would be interested in what they are saying, otherwise they are going to get drowned out by the noise in something big like r/iama.

Which means that the only people who are going to do an AMA on a big, general subreddits are mostly people who have a lot of money and influence to sell things to the biggest audience, like to promote a major blockbuster, for example.

So, if we have a big Last Week Tonight fan community on Lemmy, yeah, let's welcome John Oliver there, but he's not going to come to help ex-redditors spite promote Lemmy, what's in it for him?

Since decentralization is the way forward for the Fediverse, AMAs should be decentralized toward the community level anyways, and maybe with a dedicated community to aggregate them across the Fediverse, having a centralized instance solely for AMAs is what led reddit down its current path.