I think the current hardware for Lemmy.world should handle maybe 1M users, if the Lemmy software is tuned.
If it should grow more, we need to look into horizontal scaling with Kubernetes.
But hopefully there will be more and more servers so the users can be spread more.
Thanks for hosting Lemmy.world! Does Lemmy use a database? Until the software gets horizontal scaling capability, could we use a central RDS so the load isn't on the EC2 instance's CPU? Then we can use load balancing between multiple instances that pull from the same DB? Obviously, the db instance is still a limiting factor.