I just found out that piefed has feeds, which are a bit like the custom listings i was referring to.
Example: https://piefed.social/f/space@feddit.online
Has the communities:

Everything about Lemmy; bugs, gripes, praises, and advocacy.
For discussion about the lemmy.ml instance, go to !meta@lemmy.ml.
I just found out that piefed has feeds, which are a bit like the custom listings i was referring to.
Example: https://piefed.social/f/space@feddit.online
Has the communities:

Feeds indeed definitely help
I'd also find this handy! I like the idea of automatically surfacing similar unsubscribed communities. It can be tricky to serendipitously stumble upon new communities that match your interests, and this would be a relatively uncomplicated way of doing it.
I'd love to be able to add weights per-community or per-keyword too. There are some communities where I want to see every post, and some where I just want to see 2-3 posts each time I open Lemmy. Scaled ranking goes a long way to addressing this, but I still miss things sometimes.
I've heard today about the webring concept and i think it describes well what i want:

So, basically, sites all linking to each other, but instead of it's separate websites, it's separate communities on the fediverse!
Test