cstross, 
Some thoughts on spam:
Right now it's a single idiot running a scripted Joe Job. But we know how spam ecosystems develop. The next steps are inevitable.
Next, someone will release an activitypub spamming script. It will hammer on servers to create throwaway accounts then use them to post.
This will drive a bunch of small servers off the fediverse and cause acrimonious defederation squabbles.
Surviving servers will limit sign-ups, requiring proof of humanity (or identity).
/1
