
I feel like the Fediverse hasn’t yet reached the Eternal September moment, and I’m happy for that. A smaller footprint means we get to have our own culture.
On the other hand, even though it means losing this culture, I would like to see greater general adoption of the fediverse and decentralized social media in general. Sure, there will likely be some big-name domains serving fediverse instances, the same way email is primarily served by Gmail et al, but anyone should be able to spin up their own instance and interact as well. I don’t believe Internet communication should be locked behind various walled gardens, and people should re-acclimatize themselves to a version of the Internet where anyone can host and contribute.

Reddit does work differently and they would have to implement the ActivityPub protocol in order to federate, which would be a lot of effort for them.
The bigger thing is, ActivityPub is an API protocol. So for example, by knowing your username and instance I could call a particular API endpoint on your instance and get, just as one example, all your “outbox” messages - everything you have posted, the tags, actors you have sent it to (people or communities), etc. The reason for the large recent Reddit exodus is that they shut down their API because they do not want people to be able to easily pull all their data. So they would absolutely never implement ActivityPub, in my opinion. They want to remain walled off.