Suggestion: Allow people to view the "home page" and/or a list of communities of other instances from your own instance
For example, I'm interested in programming.dev. I want to see what communities they have and how their local posts look like. Therefore, I thought it would be a nice idea for there to be a button which you can press to just see posts from that instance. This would be the same as simply navigating to that instance's homepage, but with the added bonus that you are logged in and can interact with posts.
Another interesting idea would be a place to view a list of communities local to that instance. For example, a "sort by instance" button could be added to the community tab, where instead of only showing local and all communities, you can also view all communities local to an instance (such as all communities on programming.dev.
I like the idea of custom feeds that allow adding users, communities, instances or tags. That way you can personalize better what you see. So adding a single instance to the feed would be like looking at the local feed from that instance, but you could make many more kinds of feeds.