Most communities are not the sole community related to their topic, there are really often other communities on the same, or similar topics.
An example: there are a tonne of art related comunities, but only a small handful of them have links to other related communities.
It would be great if there was more of a culture of propping up semi-related communities. This would be particularly useful for helping more niche communities get rolling.
I disagree, in my experience this tended to lead to the whole. “This interpretation of our niche is better suited for our sister subreddit so your post has been removed”
If there are clear distinctions between them, this is a good thing IMO. If I sign up for a community, I want to see content that’s on topic. If I see too much unrelated stuff, I’ll leave. If I want to see both types of topic, I can just join both.