"Sticking to the current UI will limit the amount of functionality insertable into bryce."

I believe you can add the most advanced features to bryce without ever changing the basic UI.  Just add a GRAVITY button on top, dynamic CLOTH and FUR  buttons in object/polygon properties,  RADIOSITY and AMBIENT OCCLUSION buttons in render properties, and a MAKE SNOW button in atmosphere.

And speaking of Blender... last time I tried it, it reminded me of a new car where the brake is in the glove box, the accelerator on the dashboard, the steering wheel in the trunk,  the radio on the roof, and you can't find the gas cap.   Now if Blender power was merged into Bryce, that would be exciting.

"An Example is worth Ten Thousand Words"