I could see Google integrating with the fediverse once it reaches critical mass. Using ActivityPub for indexing ought to be more efficient than the usual web crawling.
It’s not exactly something that you can force. If X amount of users want to join an instance Y, the instance should be able to provide capabilities to host those users. Besides, horizontal scaling provides other benefits, stability is the main one - if one server instance goes down, others can immediately pick up the slack.
That’s how you die of asphyxiation