I know that many people don't like complex or intransparent recommendation algorithms.

Currently, there are "subscribed", "local" and "all" categories (at least in the default lemmy web UI).

I would like to change this to include custom topics ("listings").
They are a custom way of choosing content (in case of Lemmy listings). In Lemmy, custom listings appear just like standard listings (API-wise), just that instead of "https://discuss.tchncs.de/?dataType=Post&listingType=Subscribed&sort=Active" you have "https: //discuss.tchncs.de/?dataType=Post&listingType=list:AAAA4865698@lemmy.world&sort=Active" or something.

Listings could either be lists of communities and other listings. Consider this simple text file to describe a listing for a memes-topic: (that contains 2 communities, everything on 1 domain, and another sub-listing)

c:memes@lemmy.world
c:memes@lemmy.ml
domain:memes.net
list:AAAA4865698@lemmy.world

Or they could take their data from an RSS stream or similar external source.