I've thought about this for HN which, now that it's become so big, just has a lot of aggressive negativity and snark. You'd probably run into the same problem as Usenet Killfiles: the folks that use Killfiles would see random orphaned conversations or would just miss large parts of threads while the people that don't have Killfiles would see a mess of toxicity that would make them want to leave. Likewise if you prompt filter your experience, you'll be separating your experience from everyone else's.