Your mockup looks cool
I'm fine with integrating it into trunk. But there are some constraints you should be aware of:
1) The new interface must expose at least as much functionality as the current one. Sacrificing functionality for eye candy is not acceptable
2) Currently it is not possible to allow write operations on the library via the content server (the library backend is being refactored to make this possible, but it will be a while before it is done).
Looking at your mockup, with regards to 1), there is one problem, the number of top level categories is not fixed. Users can create custom categories/columns. So you will probably need a lower scrollable row with custom categories/columns in it, if any.
While hacking on the interface, I suggest you create a few custom columns to keep this in mind.
Also you have to remember that the content server is often used on very small screens like mobile phones, so your design needs to degrade gracefully. Since you seem to be using standard jquery widgets, that should mostly happen automatically, but it's something to keep in mind