When creating a new instrument sometimes it’s useful to temporarily solo a certain layer…the only way I’ve been able to do this so far is turning down the volume of all the other sample layers…maybe this feature is already there and I’m just missing it? If it’s not could we possibly get a solo button for each sample layer of an instrument?
I do not know if I understand correctly. You is in Keyzones?
If so, in Samples Box (left) you can select a samplelayer linked to highlight and overlay,and then edit each layers.Each layer is always linked to a sample, never mind that the layers are superposed.
I do not know if I’ve helped! 
Now (in Renoise 3.1) I think the layers can be stacked one behind the other with button “Drum Kit” (top). The problem isdismantling all created vertical (Velocity Layers). The edition layers (Keyzones) can still improve,with more useful features…