If you where to try and explain the Fediverse to someone, how would you explain it with it's different instances? As well as explain why it is better in some ways for the future of the Internet?
Seriously, though? Everybody goes to the email analogy. The email analogy really doesn't work.
Not only does it raise more questions than it answers, but it is also not a way people conceptualize social media and it generates the false assumption that the posts themselves exist as the component units of the entire thing as opposed to being tied to the format of the instance.
The thing is you don't even need to bring up interoperability for somebody curious about a specific federated app. In practice, most of the experience doesn't require wrapping your head around that part and somebody can explain the details the first time you get a weirdly formatted posts in your streams.
The wonders of interoperability are a small anecdotal thing for techheads. You don't need to think about that at all, barring some edge cases or being lightly confused by somebody posting more than 500 characters on Mastodon.
You just... tell people Mastodon is like Twitter or Kbin is like Reddit and let them have at it. A million federation evangelists will answer their questions in three months when they ask how come they got a notification from being quoted on a different platform or something.
Yes, but crucially I've passed the job to someone else who is a) already doing that full time in excruciating, obnoxious detail, and b) who is behind the massive barrier to entry that is making an account and starting to use the service.
By that point the people asking the question already know the basics and are engaged. At that point the problem is stopping people from scaring them away by overexlpaining federation, not getting them to understand how it works. It's not the same.
Constantly, through obtuse similes that only make sense if you already understand what is being explained to you and mostly to each other, rather than to anybody who wouldn't know.
But still, by that point you have an account, so you're already set.
Okay, look, I'm being mildly facetious here, but the genuine, serious point is that the differences interoperability introduces aren't that big of a deal in common use, they're not a selling point to average users and there are plenty of readily available resources to catch up after the fact.
The selling points should be about the features and content. You seriously don't need a tutorial on interoperability before making an account, just perhaps a suggestion of a good default instance to join on the service of your choice.
I know it's more complex, just if you are trying to explain what the Fediverse is to someone who's older or someone who just thinks it's another social media instead of a whole new way of looking at the internet it's hard to explain to that person who isn't really looking actively for an 'alternative' for 'x' platform.
And anyone can set up their own facebook/twitter site and you can choose which one to sign up with. Then you can interact with other people on other facebook/twitter sites.