It’s an issue that could be solved within lemmy where communities with the same name should be able to merge and show each others content.
This is bad idea though, unless if it’s an optional feature that the users themselves choose to activate (e.g similar to multireddit, but you don’t have to manually curate the communities yourself). Imagine the same community from two opposing instances (e.g. blahaj and hexbear) somehow got merged by default. That would be an absolute shitshow. Also, how would moderation work? Those communities often have different moderation rule. Can mods from one community remove posts from another community with the same name? This would also be an absolute shitshow.