Render tiles order follow mouse

I've seen this in a few render engines, and it is super handy. Often times, when doing preview renders, you are interested in a few regions more than others. Rendering in some sort of spiral order, starting at the center is great and all, but if you just want to spot check how your ground shadow is looking, or if you have enough traces on your refractions when going through several layers of glass, etc, you may have to wait a while to see that.

So a solution is to have the order follow your mouse. If the mouse is over the render window of course, and it would have to be based on a slight timer so it only queues the next frames if the mouse pauses. If the mouse then leaves the render window completely, it would either leave that spot as the center of the frame, or default back to the image center (if that is more efficient). Either way, it would be an option.

It's a great tool because you can sort of "paint" render regions while you're doing a full render.

Of course, blender could make it even Better by doing something cool like letting the user actually Select starting tiles for current/future renders. Selecting multiple tiles could split every other tile as an order which would work well if you're doing a large render with 2 main points of interest mixed with smaller tiles. Those areas of interest would clear up first, instead of waiting extra time for others.

I'm sure some of you will think the feature is dumb. It's not for everyone, for sure. But you just wouldn't have to use it, because it would be an option. I used it quite often when I was using vray, rendering in 3dsMax.