To me local timelines only make sense if the instance has a very clearly defined group with some kind of shared access, e.g, a company that has an instance for use by its employees, or a club or organization have some kind of membership. Unfortunately Mastodon's culture seems to about aggregating around instances with a very loose sense of "community" - e.g, "photographers", "open source developers", "lgbtq allies". To me this is - quite frankly - stupid. Not a day goes by on /r/mastodon where someone asks "is there an instance for X?" thinking that Mastodon instances works like subreddits.