It is probably due to a number of people stopping using their alts after some instance hopping.
Also a few people who came to see how it was, and weren’t attracted enough to become regular visitors.
Curious to see at which number we’ll stabilize.
Next peak will probably happen after either major features release (e.g. exhaustive mod tools allowing reluctant communities to move from Reddit) or the next Reddit fuck up (e.g. removing old.reddit)
Stats on each server: https://lemmy.fediverse.observer/list
Propagation and agglomeration is a problem for clients not servers. Server only need to propagate a “we have new stuff” message and it’s up to the clients to pull it and cache it. In any case, users should be able to click /c/books and see the content of all /book/ on all instances in a single location. Unless most users can do this with one click, there will not exist a fediverse wide community.
That’s entirely a design decision, and it will drive user experience. Technically there is no need for any server, besides “bootstrap” servers, and all this could run over p2p, on clients only.
But the user experience would be vastly different. For instance, see Tox vs Nostr. Tox didn’t spread well, because on mobile (the only target where IM was really lacking), the P2P aspects drain both your battery and your data plan.
Same goes here. Yea, it can be a client side implantation, but then you cannot expect it to be a unified experience across clients. So, it can be done, as-is, with client implementation, and the experience will vary drastically from client to client, and from uplink to uplink. Or, it can be done partly server side, with efforts aimed at minimizing the processing needed from mobile terminals, using metadata to provide events and general control hints.
But whatever, I’m not involved in the fediverse or in Lemmy, so this isn’t realistically something that will impact me much. If, as a user, I find that the experience is too tedious, I will simply disengage progressively, and allocate my time to other sinks.