By turning their site into this: https://i.imgur.com/TtVAiMN.jpg
That's what a new visitor to reddit.com would see, as of about a month ago.
Im hoping for a ActivityPub[1] reddit clone (or maybe I will start writing one myself if I have time). At that point it will be downhill for Reddit.
Imagine, even HN could be a federated node...
Isn't that the sort of thing Mastodon is about or are you picturing it differently?
I think Mastodon is more like Twitter and PeerTube[1] is like Yoututbe. Both use Activity Pub.