Good point, I added the bark shader to the “organic” category. 
The download size is of course something to keep an eye on. Despite not having to uv unwrap the objects, keeping it mostly procedual textures also make sense for that. – If the library grows too big, it could always be an additional download for an extended library of course.
What should be included in the BfA download could be “the ESSENTIAL library” (which is also a great name for it.^^) – Maybe it is enough to just include some placeholder textures, if it is treated more like a toolkit of presets, that the user plug in their their own textures. – In that regard one wood material (in some variations, like glossy, matte, raw) would be enough, the rest relys on the creativity of the artist to fill in the textures as needed.
Edit: The “ESSENTIAL” and the “EXTENDED” library could be good names for these features.