SilkTone
You can already do the same thing with Melodyne (or AudioSnap?). I have Melodyne Editor (so it supports polyphonic material), and I've used it more than once to move or to stretch a single 12 string acoustic guitar note that had a small timing issue. It is amazing that you can move or stretch just a single note in a sea of overlapping notes (which includes all their harmonics as individual blobs).
But to tweak the overall timing of a performance, VocalSync would probably be useful. Maybe given that people might eventually use it for more than just vocals, it should have been called AudioSync or something else more generic?
This seems to be more of a convenience tool. As you said Melodyne would work as would Audiosnap but would be more work. In melodyne to tighten two chord parts you would even need the polyphony. Just the timing stuff to move the blobs closer on the timeline.
The nice thing about the VAlign seems to be how simple and quick it is to use and I do certainly hope it will work well for guitars. The fact it is variable and a region FX too is great because even though one might want to tighten guitar tracks together you don't want them TOO tight for some stuff thus losing the fullness produced by two distinct performances.
If it ISN'T honed all that great for guits hopefully they'll release another version or a preset more suited for such tasks. It would be immensely useful to me personally. Something I'm currently working on would benefit greatly. There are spots where I am playing single note riffs where I want those notes on the layer tracks to be as tight as possible but then there are chunky chord parts that sound better with a bit of wobble. I'd apply it the effect to different degrees to the different areas. Currently I do a pile of takes and then match the best because that's easier (for me but I'm a good player and a sucky engineer) than fiddling with timing correction stuff in Melodyne or AS.
However for the stated/dedicated purpose of vocal correction it would still be invaluable because my mics are all kind of crap so to get a good sound I have to mix and match with multiple takes using the various mics. It makes it very difficult to make that sound like ONE track so this could help with that.