I believe it has been done a few times technically. I don't have any of the past links handy. I believe the challenge would be the human capitol to operate and moderate the site and of course the servers, server hosting and network costs
links, cdn, anti-ddos, etc... So the missing ingredient is either a VC or philanthropist that can see potential gains from replacing them.
Reddit has somewhere between 800 million to 1.6 billion accounts with about 50 million active concurrent daily users/bots. Whether human or bot the platform would need to scale to that amount and quickly remove illegal content at a minimum. Add to this the replacement needs to offer compelling reasons for the existing user-base to migrate.