One example for this that i have been thinking of is chat. Instead of having 15 different apps, we should be able to choose which UI we want to use, and then that opens the chat streams. Kind of like email, where you can use any client. However most big companies would fight this every step as they loose control.

Edit: I envision it a bit like streams of data that you can subscribe / push to. Think RSS mixed with a pub/sub type of model. You would subscribe to the hackernews datastream, and submitting articles and comments are done using push. The push message would have some predefined metadata fields that are obligatory (article url, title, summary or comment text).