Input during the design process is a tricky thing. You want constructive, well balanced, unbiased criticism, but it's hard to tell where other people are coming from. And no one likes a backseat driver, too many cooks spoil the broth, etc. That said, I'd hate to have everyone coming down like a ton of bricks on my baby after the fact.
The Theremini seems to be a perfect example of exactly the type of thing coalport harps on re. blind engineering producing awkward, nonsensical musical products. But I also agree with FredM regarding the relatively minor limitations of a competent, detail oriented, open to suggestion developer on the right track, particularly if they have some kind of musical background.
coalport: have you tried the close pitch hand calibration position ~5" away? This seems to help linearity a lot. I hold out little hope that a SW update will positively influence the sluggishness, though I'd be happy to be wrong.