There were techniques we were working on prior to the ISPs neglecting them.
One such technique was a crypto method, similar to what has been recommended in reducing spam in emails. The client has to do some lengthy crypto transform for the message(and NG) they send. On average, it would take .5 sec to generate per message. Small amounts of messages would get through, but spammers would be unable to bulk-send without some sort of supercomputer.
The appropriate algo could be agreed up and updated to increase the amount of time for the message. Even in worst cases, you're utilizing a slow computer for a second or 2. Solves the spam issue.
On average, it would take .5 sec to generate per message
So if I want to post from a mobile device, I have to wait considerably longer? And if I hijack a lot of computers for a spam farm, I can send as much as I like?
Spam is not only defined by bulk. You still need moderators, and that means a process for establishing and maintaining who moderates a particular group. You need people to delete the child porn and the death threats, and that means a process for deletion. (Signed cancels were a pretty good solution in the end). You probably want some means for identifying persistently troublesome users and their sockpuppets from legitimate new users.
You need hosting so that people can effectively access it despite firewalls and on mobile devices. You need a means of paying for that hosting.
As someone who hung around a few usenet discussion groups well into the 21st century, the problem was less "spam" and more "trolls and kooks". It only takes a very small number of people to completely disrupt a group, and no, "plonking" was not a solution that worked. A new usenet would need some sort of moderation system.
Because that is what Reddit is serving, as well as the previous board sites the people came from.
Usenet was decentralized, no logins, and some were moderated. But this is what the people want, yet they do not know the name.
Most NG servers are shut down.