I don't know. Maybe over time people will settle on a certain set of common hashtags and then people can have following lists that include and exclude hashtags on a per-person basis.  So instead of following a person, or following a hashtag, you can follow something like "mike & !politics".

I think nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn has done the most on custom feeds. I haven't looked deeply into what he did yet.