Hi,
I guess it is not to difficult. But sometimes I get surpriesed by the easiest things.
Raytraced DOF would be very easy to implement but it is quite slow.
A good postprocess DOF would be a little bit more tricky but on the other side much faster. And postprocess is good enough for most scenes.
DOF is definitely a 2.x feature. I will add it via a camera tag once I start with it.
By,
Martin