Can you add one to your list? Linking posts across instances? Like you can do !community@instance and the community will open viewed through your instance. But for linking posts there is no such equivalent. Like if I make an HTTP link it will be through my instance or possibly the one the community is hosted on which would be annoying for users of other instances.
Also, linking communities across instances is possible already, but you can leave it up since it’s confusing. I still see a lot of folks try to do the reddit approach if c/community