So, synth replace would be like you were using Vienna and decided to use Hollywood and want to replace the synth in the rack without having to copy or drag all the MIDI notes, set up the track level and panning, reverb, etc.? That would be good for a lot of things (e.g., RealStrat to RealLPC, change pianos, etc.). Replace drummers could be tricky if the tracks weren't laid out the same.
I am surprised by VS-700 support. Not sure what else they could do to integrate beyond what is already there, but maybe something cool.