If only there were some extensive property of matter we could multiply with the temperature to compute a weighted average. That would be massively helpful.

YYYY-MM-DD is the only reasonable way.

Along those lines, what if communities could suggest other related communities, and clients could (by default, but optionally) also show posts that the communities your subscribe to recommend?

It’s a little like soft federation, but on the client side - or, think of it like an automatic way to make multi subs while still allowing users to change it, and giving mods a less nuclear option if they don’t like how a community on another instance is going.