I also fear that the centralization of the web to a handful of websites has made a revival impossible. If 80% of your stumbles are just reddit posts or imgur links, whats the point?

That you can exclude them?

People seem to have forgotten StumbleUpon had a pretty decent configuration page where you had to manually select what topics you were interested in, and that submitting new pages wasn't as simple as just submitting the URL. On top of that, I'm pretty sure I remember a "block this domain" option if you clicked the arrow next to the thumbs down: https://i.sstatic.net/VLS4c.png