The final decision

The decision are taken.
After some days (well weeks) thinking on the dilemma, finally I have changed to WWJ API.
My own Balloon Core API remains in a stand by state and more probably it will become a mere hobby on creating a 3D scene graph than other thing.
The WWJ is populated by more people than me alone. WWJ evolution is quickly than Balloon Core API and more powerful :( than it.
As a result and in addition to use WWJ in my project, I have started to create contribution. Now I am finishing testing two:

• LayerSet: Insted of have a layer list (in the model) it allow to have a tree of layers.

• Temporality: I have created a couple of classes and hacked a bit the WWJ to allow associate time properties to renderable object. Also I have created a simple timeline layer (based on the ScaleLayer) to show the time position.