Here's the idea: it would be really great if data could be linked, referenced and exchanged in a standardized, application-agnostic way among web applications.
We should raise atomic data to the rank of resources, and make possible to link them from HTML documents like we already do with images, videos, CSS and JS scripts, and soon HTML components. Just reference it and the browser will be in charge to retrieve the actual data and compose the final document.
This would be an awesome way to leverage the web platform true power: linking!
The closest thing you can do now is log in an app using Facebook/Google/Twitter/Other, but the linkage between the identity provider and the application is usually weak and ephemeral (I'm logged in a lot of applications where my profile picture is still an old Facebook picture that wasn't automatically updated).
And I'm not talking only about basic personal information, but also data like music listened, fitness activity, rates and reviews, messages, wider concepts of "post", "like" and "sharing" and so on. Just think about the richness of the schema.org vocabulary, it covers an unbelievable range of data types. Infact, the majority of the needed formats and standards are already available (RDF, HTML5 microdata, JSON-LD, XML, HTTP protocol, ecc.) and more or less diffused in the web community.
Apps could be a lot more powerful: from the UX perspective, it'd be great to just have the user to approve your app and then having an extremely rich collection of data ready to consume. From the users' point of view, we won't bother anymore about "being locked" in an app, because well-crafted apps will become just interfaces to access our data, that lives above (or underneath?) every app.
Different apps, despite manipulating the same type of data, really manipulate different data because they're not compatible. You can't just export your Whatsapp chat and open it in Hangouts, much less access it solely by switching app. We are used to this behaviour and as of now people don't expect apps to work differently, yet the discomfort is real.
Two concerns remain to address:
User's privacy: apps shouldn't be able to access all the user's data straight away. Period. The user should be able to allow or deny access to his data, and to limit the scope of the allowance. The way Facebook API now works is pretty good, we could figure out something similar using maybe the browser itself as a mediator, like some HTML5 APIs now work (Location API, WebRTC and so on). At last, users will have more control on their data because linking reduces duplication. If I can manage the source of the data, I can manage how this data is used in all apps referencing them.
Derangement of the app market: app developers could argue that such an easy exchange of data and aggresive standardization could harm the app market, since apps couldn't lock in users anymore. Well, I think this will harm only bad apps, whereas in the long run apps that are not evil to the user (because locking in is evil) will be favored and preserved. Quality will be rewarded, and we'll assist to the same process that hit the browser market some years ago: fast, lightweight and standard-compliant apps will have a neat advantage over the competition. I see this process as really beneficial to the software industry, at least ethically and philosophically speaking. Maybe advertising will become less profitable, and maybe this will led to less free apps on app stores, and this would in turn be bad for the user, but would it really be? Actually it isn't the first time that we talk about apps as mere interfaces to some freeish dataset, just look at Twitter clients. And Twitter is not filing bankruptcy anytime soon.
In the end, I think that if worked out cleverly (that means "if we just think about it") the web of data could be a huge leap in the IT sector, unleashing a wholly new range of possibilities, like the IoT is going to do soon, but bigger! Because data is the foundation, and improving the foundation means improving the building altogheter. And it's going to be a pretty awesome building.
(What do you think? I'd like to confront with other people on the topic, please assault the comments form)