i don't have extensive experience with forest pack or forest color so correct me if i'm wrong, but it doesn't seem that the forest color texture works outside of a forest pack system.. the point of a vrayMultiSubTex is not necessarily for variation across multiple objects in a system, but rather a way to control a single material with different texture maps for different ids. this makes it very valuable no matter how objects are being used (whether they are used in a forest pack system or not).
there are also other incompatibilities, such as the fact that vrayMultiSubTex supports 20 textures (probably more in the future) as well as ObjectID support (whereas Forest Color only supports 10 textures and only material or "element" id).
if the forest color texture worked outside of forest pack, that would help the situation, but vrayMultiSubTex also has the advantage of being part of the renderer package as opposed to a separate plugin, so if an asset and its material are built using it they are guaranteed to work regardless of whether the user is working with forest pack or not. (although forest pack is a valuable tool, it is not as significant a part of a pipeline as the renderer). i understand the developer advantage for a separate texture (as well as being able to add cool features like the "Tint" variation in forest color), but from a user stand point it seems that support for the renderer would be even more desirable.
is support for the vrayMultiSubTex something difficult to incorporate?