Hmm, some misconceptions here.
*GPU is not always the fastest rendering method (yet). Otherwise, what would be the point of keeping the other render modes?

BiDir on CPU is still better at dealing with more difficult lighting scenarios, such as your scene.
I tried your scene, and it's probably the slowest rendering interior I have ever seen.

You have made it incredible difficult for the sunlight to "find its way" into the room, and the whole room is lit up by those small light patches. I would say 9 hours is actually a reasonably good render time considering how it's lit.
I would try adding exit portals to help connecting the sunlight to the camera. Use that together with BiDir and you *might* get better render times. Another way to improve rendering speed would be simply removing the glass windows and the brick walls and architecture that's blocking all the sunlight, and maybe putting the sunlight at a lower angle so that it enters the room properly.
* GPU currently doesn't work with BiDir.
* GPU currently doesn't work with Exit Portals.
* Regarding "hybrid rendering" you've basically answered your own question. Under OpenCL, you can use CPU + GPU to render (although the main rendering power will definitely come from GPU), which technically makes it hybrid, right?
Eneen: Nope, I asked Ono but got no answer.