All I can gather from their video is that they're trying the internet again with a different approach (built-in encryption, tools to far more easily build decentralized applications, your data is yours, and a point about API stuff that I don't quite grasp yet.)
Their goal is to be a self-governing digital republic, whatever that might mean.
As the guy says in the end, it's not up to them what urbit will become, it's up to us (the people who develop for urbit).
That's how I understood their video
Soooo... I'm not too sure why building (arguably?) better tools would result in a "better" internet. Additionally, I'm not too sure what the advantages are for end-users for decentralized applications.
So to conclude, it's up to the developers to find valid use-cases for urbit. Just like how it's up to developers to find valid use-cases for ethereum. Decentralized toolchains (like ethereum, other blockchain-things and urbit) are in their infancy, nobody really knows if they'll sprout useful use-cases or not.
Tl;DR Experimentation and uncertainty
From reading the whitepaper it seemed like they were building a distributed network where everything is somewhat abstracted.
I thought Ethereum was silly and pointless but I at least somewhat understood what it tried to be, this is like literally something that looks to me that came off https://www.reddit.com/r/VXJunkies/
It's a decentralized internet, where your computer is the server, and it communicates directly with other computers by calling directly to their addresses.
As a result, e.g. your facebook data is stored on your computer, and other facebook users call your computer for posts.
Because the data is stored locally, and called through relatively universal APIs, any app can be written to call and display from those APIs, combine them, and let them inform each-other in any way you desire.
You can put your facebook in your reddit in your gmail.
That all runs inside a VM which ties your data to your address, so your identity (real or pseudonym) is singular, and uniform across all apps. This creates a real cost to ugly behavior, like spamming or trolling, as addresses are too limited to burn through willy-nilly.
Apps running on that VM are coded in a rather confusing functional language. Lots of people think he made it that confusing to stop newbs from writing for it.
I bought a star.
As for the infrastructure, that's a rather more esoteric concern. It needs a distinguishing term.
My new one-line description of Urbit: "Diaspora in INTERCAL on a blockchain by VXJunkies."