For that to happen, I believe that interacting with people from other instances and moving your community and account from one instance to another have to become possible / easier.
At present, people flock to the instances with most users as those often have more local content (local content is generally easier to find than federated content) and they often have a smaller risk of shutting down. If I create a community on a smaller instance, the chance of it being found and interacted with are also much smaller than if it had been created on a bigger instance (because of, as I said, local content being user to find).
Sure, I can create an account on myfirstlemmyinstance.com (example URL, not an actual instance) with 10 users, but if my instance decides to shut down, my community of, say, 500 users will now have to move somewhere else and all old content will be deleted.
There’s a homelab community, https://infosec.pub/c/homelab@lemmy.ml