With the Utility tracks you can generate any section. If you could move and crossfade them easily you could have the sustain going into the next chord: Oohs-Ahs-crossfade.mp3
<< If you could move and crossfade them easily you could have the sustain going into the next chord: >>
With both Utility Tracks and the Audio Editor Track, BIAB already automatically crossfades and the duration of the crossfade can be manually adjusted by users so it's possible with some experimentation this can be done. BIAB's automatic crossfade isn't as precise as your demonstration but I wonder how BIAB would handle the sustain using its automatic crossfade?
An alternate method giving the user more control to do the operation is to use two tracks and manually create a crossfade by one track fading in as the other track fades out and then bounce those two tracks onto a Utility Track.
Same deal with midi, just have a view button in the Audio Edit to edit the midi track. These suggestions may not get implemented til way down the track, but I'm just putting the ideas out there as I won't be around here forever.