There's a few threats to the Fediverse.
Here's what I think they are:
1. Google extending their dominance into Fediverse search
2. Jack Dorsey's crypto obsessiveness (see Nostr)
3. Cloudflare's Mastodon competitor (Wildebeest)
4. A16Z investment in Towns -- which is just Matrix with crypto pixie dust
5. Developers' myopic focus on Mastodon to the detriment of the rest of the Fediverse