Pertaining to what Errikos said, and if we take notation off the equation, this VSL DAW becomes much more feasible. If composition is done elsewhere, let's say in Sibelius, or another notation package, and the user does not expect accurate playback from this package, he could then import the file to VSL DAW, in a manner that the notation (would have to be MusicXML) is automatically converted to the appropriate midi-data.
I for one, have gave up producing mock-ups for one reason. I can not put myself into the burden of setting up a DAW and then effectively recreating the score I already composed. To me this absolutey kills the joy of composition, and only recently I decided to try it again. If the DAW was already preconfigured to work with the VST I use (VSL in this case), half of the work would be already done, creating a track FOR an Oboe, would be akin to creating a staff in Sibelius for the Oboe of Sound Essentials, no setup required.
The other half of the work, if we come from notation, is getting notation symbols to become midi lanes, and I believe that can be achieved even without the VSL DAW, just by having an MusicXML to Midi translator which allows you to set how each articulation should be translated to midi.
Anyway, I agree, that without notation, the DAW becomes more closer to reality.