So far I just handle it manually. I've dialed in pretty good preferences for incoming content, (for example, using regex-based whitelists and blacklists to weed out material I'm not interested in from channels that aren't already organized into appropriate playlists) and when I browse the videos directory to find something to watch I delete things that have been sitting there a while which I don't expect to get around to.

There would be a lot more work to do if I wanted to "product-ize" the tool, and periodically youtube breaks it by adding a new feature or moving something around. For personal use, though, it's very needs-suiting. The whole approach is also less of a tempting distraction than browsing youtube itself, so it's easier to manage how much time I spend watching videos. If I ever run out of content, I just go for a walk, or read a book!