Fractal artists: what do you want in a fractal program?

[lxh]

For instance, the tools in Cinema 4d that control ...

If you like all the benefits of C4D why don't you use Voxelstack?

But to stay realistic, in the special case of Mandelbulb 3D i could imagine:
Cylindrical projection for the background sphere and a horizontal flip option.
Volumetric light and shadow - or light and shadow option for dynamic fog.
An enhanced color adjustment for reflection alpha and maybe translucence.
And - to be cheeky - a node-like formula management system to combine, position, scale, rotate, color and blend different hybrids.

Edit: I forgot .. 16bit Z-Buffer