Science Inc. owns it

Or whoever. If it's a free service, it's subject to monetization.

Why does it matter that much though? It was other issues that made Delicious fail, including that Yahoo sucked at acquisitions back then (they have since improved).

Depends what you're bookmarking. Some people value their privacy. A bookmarking service probably knows almost as much about your political affiliations, your sexual orientation, etc as Facebook or Google does, after you use it for a couple years. I trust Maciej not to exploit that information.

So it's not really about whether another bookmarking service can deliver or not, for me. It's whether they're faithful steward.