We would very much like to have collections generated this way, for example showing old library content. For instance we could have a search that generates a collection of all collections published in the month august of the year 2014, sorted descending. Then i could manually make the parent collections containing the year and months.
An other use could be loading all articles with a specific keyword, or from a specific department.
In may ways this could be done in a similar way we do the card mapping today.
This is actually one of the core ideas we talked about when first discussing DPS 2015 with customers (before we even started building it). We call them dynamic collections and they're absolutely a cool idea. A lot of the infrastructure of DPS 2015 was built assuming they would exist down the road too. For example, you'll notice when you hit a browse page that it doesn't matter how many items are in the collection, we'll still load it super fast and handle it fine.
At any rate, it's on our list of things to do, but isn't something we'll get to this year due to other priorities.