The problem is that binaries are transferred in a non-binary manner. Base64 was the preferred way. Except it was also used to push images back and forth as well for pertinent conversations.

For any method of communication, you can transfer content that someone else tries to prevent.

Upper bounds on per-user bandwidth would work. Implementing this is nontrivial, but it's an essentially easier problem than spam.

Upper bounds on per-user bandwidth would help. Though for significant messages, one still has sock-puppet accounts (or aggregates of like-minded individuals with copies of the source message pooling their resources). And, of course, upper bounds create knock-on restrictions (should the system be allowed to transmit public-domain large-volume data? A bandwidth limit blocks that "valid" use too).

It's fun to game-theory how such limits can be broken.

Who cares about piracy? It exists over HTTP, too, and in a far greater volume than a modern USENET-equivalent could ever hope to achieve, and it's not like ISPs need to be sucked up to anymore: they've already taken their ball and went home on this matter, proverbially-speaking.

They were uuencoded. https://en.wikipedia.org/wiki/Uuencoding

Unfortunately, technically banning binaries merely means binaries will be transferred in a more spacetime-inefficient manner.

You can mathematically prove atop Shannon's theorem that if the system can transmit comprehensible text information between two users, it can transmit binaries. Worst-case scenario, the users could use the text information layer to just say 'one, zero, one, one, zero, one' at each other, etc.

(Socially banning them can certainly "work," in the same sense that social banning works in any context: pushes it underground out of the moderators' lines of sight. Depending on what you're trying to accomplish, that can be good enough).

I have given this some consideration, and what I ended up with is super low tech: require a user registration where users can't just sign up for N accounts and limit all accounts to 10 MB a day. Too little to share any meaningful binary data and way more than a person can type in a day.

It's a good idea. What stops a user from registering for N accounts? How do you tie one account to one human?

In my original consideration you could only sign up with government ID -- actually the original problem was what to do prior to the day reddit banned your community, so that you could keep going.

In either case it was pretty trivial to picky bag of existing IDs, if I ever solve that for the general case, you will find out.