What about a generic My Hacker News with a classifier trained on each person's personal "I want to see / I do not want to see" preferences? :>
Is it specifically subreddits to avoid? I completely agree that subreddits are a terrible implementation of user-content customization because they force items into a single-parent hierarchy.
However, categories that filter content according to different weights would be quite useful. By pre-selecting these categories and thus pre-computing them, it would even be reasonable to implement (actual per-user filters might not work so well in real-time).