I wonder if, should mastodon succeed, we'll see a gmail-ification.

Like, email was federated.
Then spam became a huge problem and so major ad-supported email providers blocked email from anyone sketchy-looking. Everyone flocked to major providers because they were free and had less spam. Increasingly, 99% of spam came from non-major providers so major providers understandably blocked most mail from small email hosts. Now most people use a major provider and email is only barely federated.

That said, one could argue the root cause here was spam. Anyone can email you, so that hard problem needed a solution.

Mastodon should have much less of a spam problem - I can just not follow people I don't want to hear from. Maybe without that compelling need, we can continue to have a wide variety of small and medium instances out there!

@kkuchta At a minimum you can reply a fair bit. I'd expect reply-spam and its close relative harassment to benefit from defensive centralisation. So: GMail-ification's not unlikely if we want good moderation, something resembling a cross-server block, etc.
@kkuchta You're already seeing people talk about blocking specific Mastodon instances (not a bad thing.) But there are gonna be trivial ways to get around that if people want to. Centralisation makes those blocks hard to get around in a world where you can always stand up a new server. As you say, like email.

I should learn how the visibility rules work around here. Could one just hide replies from all users you're not following?

But yeah, I agree that blocking instances is likely to be about as effective as blocking email domains. You could allow-list specific instances that are known to be decent, but then you have pretty much the email server problem.