Combining communities should be a front end feature… Allow users to merge their views if they want. But it should not be enforced at the backend or federation level.
Eventually there will be third party apps which can do this merging in their interface if someone wants it.
I agree with this. The grouping should be a front-end feature based on hashtags, as someone else mentioned, instead of the community names. Alternatively, there could be lists that you can simply copy and paste to create your own multireddit, eliminating the need for hashtags. However, considering that the original issue was already on the lemmy-ui, I'm not sure why you brought up the backend.