Then it's federated, so they're still using "decentralized" wrong, which would imply direct client<>client communication (decentralized), rather than client<>server<>client (federated) communication.
Embrace, extend, extinguish: is a standard playbook for monopolists and oligopolists everywhere in tech.
1. Make "cool corporate mastodon server" that all the cool kids play on.
2. Extend the masto code with proprietary extensions for better features, but DONT SHARE CODE
3. Convert people on other masto instances cause they don't have "cool feature".
4. Users flock to "cool masto server", and mastobook is created.
5. Other servers either try to play catch-up or close. A few holdouts straggle on.
6. Shitty company successfully proprietizes a federated system.
Email, another federated system, has nearly gone this route. Sure, you can make your own mail server and do all the right things WRT spf/dkim/dmarc. But when most email is through gmail and outlook.com and they decide you're bad, you're not 'running' email.
People said the same thing when Tumblr added ActivityPub.
The most likely situation is that the fediverse would spot this tactic and mass de-federate anyone who tried it, so that bad actor would be left making their own island and any investment in federation would be lost.
It doesn't make business sense to try and EEE the fediverse.
I think more likely is that few people would really migrate in the first place. What killer feature would do such a thing? People just make accounts where their friends and interests are. I guess Facebook might promote it heavily and network effects will get new people on it, but this wouldn't really affect other instances, I think.
XMPP is a better example. XMPP is decentralized IM, and was gaining some popularity amongst techies (e.g.: people like those reading this website) about 10-15 years ago. It's well documented, an actual standard, and plenty of extensions for extra functionality. Video calls worked okay around 2010/2011.
Google Talk federated to XMPP, and it worked well for quite some time. I had my own XMPP server but could talk to people who were using Google Talk, just like I could email people from my email server to their gmail account. It was wonderful! I had some friends on legacy networks like MSN and they shifted to Google Talk which I found great.
My enthusiasm for their migration turns out to be very naive.
Google one day said they'd de-federate Google Talk. People on GT could talk to people on GT, everyone else could screw themselves. My roster shrunk from "most people I talk to" to "two or three people I rarely every talk with".
I didn't continue XMPP much after that, though it's still a thing and continues evolving pretty well. My interest has re-sparked this year since I'm looking into using is as a gateway for other crap networks where friends insist on staying.
It's not hard to imagine Facebook (ehem, "Meta") federating with Mastodon and giving out a lot of "oh, they're actually not that bad" vibe. Many would come to use Mastodon but rely on Meta's federation. Until they decide it's time for Masto to die, just like Google decided it was time for XMPP to collapse.
