Speaking as a total newb who is about to remortgage his home to buy VI (well, that's partly why, anyway)...
Apart from a choir, which looks as though it may already be on the way, I'd like to have a second solo violin recorded by a different performer for string quartet work. I've read up on the tricks you can use to make a quartet out of 3 performers, like transposing the second violin part up on the player side and down on the midi side, but surely you're still getting exactly the same technique, plus a virtually identical tonal quality. Apart from the obvious cost angle, I can't see why the Solo Strings didn't have two solo violins right from the start, unless it's something to do with the physical arrangement of the string quartet in Austria that supposedly has the first and second violin on opposite sides instead of next to eachother, so the physical separation in the soundstage makes up for the lack of "logical separation".
Another thing that appears to be needed is an extension of the crossfade into a sort of "cross-modulation" that would allow, for example, a violin note without vibrato to be smoothly and seamlessly faded into (and out of) a similar note with vibrato. I can't help but note how quickly the crossfades were done in the tutorial video so as to avoid exposing this issue!