Dual Bore Janko Venova

I recently got a Venova and have been enjoying learning how to play it: It combines a saxophone mouthpiece with recorder fingering and a little nose to overblow an octave instead of a twelfth. It's somewhere between a real instrument and a toy, and one of its bigger problems is that while it's great in C it gets harder to play the more sharps or flats you want. Since I mostly play contra music, typically in 2-3 sharps, this isn't ideal. A Venova in D (two sharps) would be great, but I don't see this coming. If we're going to put in a bunch more work somehow, what if we went all the way to a double bore? Imagine two parallel bores with the tone holes lined up exactly, so that when you put your finger down it covers both. The holes would look a bit like the double holes on a recorder, but they could be closer together because you never need to cover just one of them: The obvious way to do it, and the equivalent of a B/C melodeon, is a C tube for the "white keys" and a B tube for the…