Kevin:
Have you seen the thread on the VSL forum about Sibelius and the new VI? The users there seem quite knowledgeable about this.
http://community.vsl.co.at/viewtopic.php?t=6891Like a few others, I just bought VSL and GS3 a month ago not having even the slightest clue that VI was coming out. I am just beginning to work through the techniques of using various articulations and other patches with the Pro Ed, Performance Tool, Sibelius and Sonar. From what I can tell, this will work very well since that's part of what that kind of set-up is designed for. Whether or not it will be useful in the "New World" of sample engines which VSL is pioneering remains to be seen.
Regarding your new computer, if you haven't already bought GS3 you might want to wait a bit. The new VI can run either as a stand alone or a plug-in to a sequencer program like Sonar or Cubase. This might be a good direction for you because it appears that Sibelius will be able to send commands to the new VI and you won't have to do all the work of programming the patch changes yourself. The issue of VI not being multi-timbral may also not matter for you. If you have a pretty decent computer, you can run multiple instances of VI and have no problem. You will almost certainly be able to run the new VI on your new computer so you're probably in good shape as far as that's concerned. The only question would then be whether or not the samples you already bought will be useful.
In any case, you might want to check out that other thread if you haven't already.
Be Well,
Poppa