I really loved StumbleUpon, but I fear reviving it would lead to nothing but inorganic traffic and malware.

It'd only work today if it was hand-curated and every submission continuously checked in case the underlying page was altered.

That said, it would work. Whether it would be financially viable is another matter, but going for profitability is ruining a lot of fun.

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?