I could see Facebook making instances as a service for sure. And hosting their own instances they could scrape data from others (which will get them defederated quick, hopefully). But just having a nice clean signup system from a company people know would go a long way to getting people to join the fediverse, and hopefully people would eventually leave
And draw the line there? Or what about instances that federate with instances federated with meta? I think defederating meta is more than enough