Forest 3 will use unlimited custom objects, not only one mesh as now. Planes is not longer included in the pack, because we have joined Forest and Planes in a single plugin. You may create a random distribution with Forest, and edit it using the same plugin.
About VRayProxy, as Forest creates a single mesh object for all the trees (it's much faster than using thousands of instances), is not possible to create a distribution of VRayProxies because they are independent objects. So, we have included a tool to instanciate the trees to the source custom object (that may be a a proxy or any other object). Briefly: yes, is possible to create a Forest of VRayProxy in a two step process (create + convert).
We have not a release date yet, the software is already finished but we are working now to improve the tree library. We also would like to include some pseudo-3D models, not only billboards, as Forest now supports multiple types of geometry. And believe me, is much more difficult to create an acceptable tree library that writing all the plugins from scratch.
When the libray will be ready, we must to write the documentation and tutorials (video tutorials, if possible). I know that you have been waiting Forest 3 for a long time, but we like to release the best product as we can.
If you enjoy watching it, i've uploaded a small test video. This is a single Forest object using the new animation features, and an animated wisp of grass as custom object. The scene doesn't include textures, only a color gradient for the wisp.http://www.itoosoft.com/test/grass/