Boost for reddit allowed the creation of custom feeds with groups of subreddits, I suspect this is harder across lemmy instances but it would make my many communities easier to navigate if I could group them together (even better if they can be grouped independent of whether I have actually joined the community).
I definitely think this would be a huge value add. The decentralized nature of lemmy makes it so that there are a lot of different communities on different instances, that all are about the same topics. As an end user, it makes sense for me to want to see posts from all these communities in a single feed.
I saw that there is some work on the upstream lemmy side on providing support for multireddits/custom feeds, but upstream discussion also seems to indicate that different frontends, like Boost, should have the apis to be able to do this client side in the meantime.
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