A great feature would to be able to change the pitch standard from A440 to A415, A466, A432... you name it. I have a number of customers' instruments I've worked on that play at a different pitch standard.
Likewise, some historical instruments were fretted to play in temperaments other than equal. I know it may not be used by the majority of your clients with modern guitars, but I would appreciate being able to set the notes for different temperaments (whether as a variety of presets like 1/4 comma meantone, 1/6 comma meantone, etc., or as a custom "DIY" setting) in order to resonate the body in the actual frequencies being played.
Thank you for your consideration!