Two thoughts: - How would you provide the functionality that hashtags do on the public timeline?

- How would users know which nodes they could trust?

I think email and Sms are pretty weird user experiences that have succeeded in part because there was no alternative.

> How would you provide the functionality that hashtags do on the public timeline?

That is what search engines are for. The whole point of the Internet is that you can build businesses on top of open protocols with interoperable implementations. Giving up on open protocols and control of data (you can't even save images on Instagram...) "because hashtags" is incredibly shortsighted.

Twitter is already a federation of servers and services. It doesn't seem outrageous to imagine another server or cluster of servers being owned by a second party.

I think we may be talking past each other here, what I mean is that federation must be strictly and absolutely invisible to users.

Perhaps I was wrong to say that federation is in principle ruled out, but I do think that it must be invisible to users. - Including namespacing usernames to nodes within the federation as with the @ sign in email.

I believe this is true in spite of the technical beauty of federated solutions, and it's exactly that beauty that's lured so many onto the rocks.

I don't think the namespace issue is as big of a deal as you seem to think it is. People are used to dealing with namespaces when they make phone calls, send emails, send a letter, get a license plate, or go to a website.