I bet they're still documenting Bryce code-base and doing occasional comparison to how things work in their other apps. (There might be some interesting tricks hidden in there, most likely with fractals, terrains, and volumetric materials.) So my guess is that other than money being tight, things are moving faster on the Carrara side because they actually have the developers to work with. (The original Bryce developers have moved on to other stuff, and are likely to not even remember things from the old code.)

Now if they want to do something cool with the UI, perhaps they should look to how Wings 3D carries over the desktop way of mouse interaction into the graphics manipulation workspace. (At least in the default Wings/Mirai camera mode.) Not saying they should completely throw away the older ways of doing things, but it be nice to have another interface and workflow put on the table. (More or less this idea: left click for selection, right click for menus/commands pertinent to the current selections, and middle click/scroll for camera controls. And for more speed in menus, middle and right click are also alternate selectors in some cases.) I find it very fast in regards to workflow, would be nice if more apps had it.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.