My impression is that the VSL user base could be divided into two categories:
1. Composers who write for "media", ie film, commercials, computer games etc. The quality of the sound library is of course crucial for this category, since these sounds will be part of the final composition. It seems that most of these composers work and compose primarily with a DAW. I guess that a realistic orchestral sound will always be more important to this category than multiphonics, scratch tone, toy pianos etc.
2. Composers who write "concert music", ie for musicians, singers, choirs, orchestras etc. Composing this type of music is usually done with notation software (or by hand!) and software libraries are mainly for playback.
My guess is that among professional VSL users 90-95% belongs to the first category.
I seriously doubt that VSL will spend time and money to develop a library that will interest only 5-10% of their customers. I hope I'm wrong.