I'm way late to the party and I haven't read the comments yet but here's my idea; the goal here is to more trying to target types of readers rather than types of subject matter, which makes more sense pragmatically given the goal is people having to read less:

Main - things everyone need to see.

All - automatically generated taking everything from everywhere and redirecting.

Articles & Sequences - the same kind of stuff you see in Main, except lower barrier of entrance, and no meetups

Entertainment - discussion threads for rationalist fiction, quotes threads, anecdotes, media recommendations, etc.

Maths & Original research - the cutting edge stuff that many people might not be able to follow, and making assumptions about more background knowledge. The stuff MIRI employees can learn from.

Discussion/Misc - current Discussion and everything that doesn't fit elsewhere.