I would like to have the option to use the vertex color, vertex alpha and vertex illumination channels available for controlling distribution.
Also, I would love to have a new parameter that works in conjunction with the Probability spinner for each geometry entry in the geometry rollout: a vertex color/alpha bias. This would increase the odds of that object appearing at any point where the alpha matches the bias.
To explain, imagine you have a terrain that is a valley with a river running through the middle. The terrain has a material that blends between Hillside and Riverside using the Vertex Alpha channel. Now it would be convenient to be able to say that pine trees have a bias for alpha 0.0 (hill top) and smooth stones a bias at 1.0 (river ). Since the bias just increases the odds, most rocks appear at bottom but a few up top, and vice-versa for the trees.
I would like to see Vertex Alpha support because of a tool I am building for a game engine pipeline where foliage is distributed by vertex alphas in a similar fashion explained here, and I'd like to be able to use Forest as an available avenue in the whole process.