Vessel is like electrum, in that you can download and use it without trusting anyone, but it's just a wallet and not a full fledged social media client like I think you're talking about.
You could definitely build a fully decentralized social media that runs like electrum though - using the same techniques as Vessel. It just won't be like steemit.com, because steemit.com uses a bunch of server side tech that can't translate into an electron app (which is what Vessel uses).
I agree with you, @jesta.