Looking at the Linked Instances, most instances have at most a few hundred instances linked. What happens when there are thousands, or possibly even millions? Could too many instances require significantly more powerful hardware, or even be impossible altogether?
In theory one day its going to be too much for our current bandwidth. We are no where near that even with single user instances.
There are ways of making things much more efficient. Piefed for example bundles up votes so the API doesn’t get hit with millions of upvotes all separately. Peertube has P2P video sharing so the more people host/view videos, it actually gets faster. Theres a ton of others. But it sounds like a future issue.