Hello,
Just a quick update: still working on v4. The changes I'm making are very fundamental so it's being quite hard and long. However, I hope it's worth it.
So far, I'm just trying to get back "basic" features with the new system, and it's still too soon to say what will be included in the new version or even a list of planned features.
The reason I'm not telling is not because I want to be secretive, but to avoid raising expectations that I might not be able to achieve. Right now I have quite a few new features that "appear" to work but it's not the first time something appears to work and later on I discover a fundamental flaw in the design (or even the concept) that ruins the entire thing...
Anyway I understand you want to know something

So, even at a risk of disappointing you later if I cannot make them work, a few features that I'm working on and I hope you will like are:
* No more waiting for the KdTree to build. I will use BVH structures that are *much* faster

* Motion Blur (although I'm not sure if this will only work in Direct Lighting or if it will also work in Photon Mapping, which adds another dimension of difficulty to Motion Blur)
* Subdivision Surfaces and Displacement maps.
Of course there will be more, but too soon to say...
Once I have a stabilized foundation for v4 that works in the different platforms (Windows 32bit/64bit, Linux 32bit/64bit and Mac OSX 64bit) I will upload the "starting" pre-alpha v4 code and some testing builds. However, that's not yet going to happen soon. I'll keep you updated.