Any post and community could be accessed through a theoretically limitless amount of instances, which also means a theoretically limitless amount of URLs.
Will this hinder Lemmy from ever coming into the mainstream? If I type any topic in Google, I will get a reddit thread that deals with that. Can something like that ever happen for Lemmy?
Would the canonical tag make any sense for Lemmy? The problem is, if you search for something your preferred site / URL is your instance. So the canonical would be different for every user?
Yeah, I think that's one of the user experience issues we're facing. Setting the canonical as the original server makes the most sense, but that would mean if you find something interesting via a search engine you have to figure out how to get it to show up on your home instance.
Like for me, since I run my own instance for myself and one other person so far, I have to find interesting communities manually. It's really annoying. Though, looking at Lemmy v0.18 release notes, a lot of new devs have made contributions and I'm sure more will help in the future. One improvement from yesterday's release is visiting a remote community on your home server will pull the community rather than returning a 404. I think changes like that are big first steps towards improving this specific aspect of the user experience.