So, you can already assign which notes are included in your own scale, and you can also enter the "Split scale" mode, for further range.. However, I think it'd make ThumbJam's sampling interface something much more expansive if you could also set the octave for each note.
Maybe I'm the only one doing this, but I have each octave fulfilling a different role.
Example; Let's say I was multi-sampling my guitar:
C1 - Mute Notes (x notes)
C2 - Palm Mute
C3 - Notes
C4 - Harmonics
With this you'd be able to include any palm mute or harmonic or any other expression you'd like, to a pre-established riff.
However, with that said, I think there's one feature that'd take it from a fantastic, to nearly perfect sampler.. Some kind of trigger. Allow me to explain the best I can; it could perhaps work on one of the control methods, x-axis perhaps. But, some kind of button or control (perhaps like the sustain bar?) to switch live between octaves. I.e, actively bring in variations in a live state to make the sampled instrument that little more authentic and diverse. The interface is already easily the best I've used for sampling, and for that reason it's sampling already sounds great. But that extra level of expression would be fantastic.