Maybe you’d get some slight flexing in the key-touches using aluminium or plastic though…which could add up to a bit of an unpleasant “spongey” feel in the action of the keys when played fast…but if you got the moulds made for the keys, I suppose you could get them cast in brass anyway - and then aluminium to see how well it worked…
Garry
We’ve now got an (almost completely separate) design blog up at http://www.mkwhistles.com/category/mk-design-blog/ which will be humming away in the background (hopefully). Please feel free to get involved - in fact we’d love it if you did.
I am afraid I don’t understand this thread at all. There is a long history of Chromatic “whistles”. They are called recorders.
Ron
shhh, maybe they’ll reinvent it 
If there were a recorder that had the sound of a whistle, I’d be playing it. The Susato wide-bore is the closest I’ve seen, but I wasn’t happy with the sound of the notes above high G. Without understanding the reasons why, I assume that the very properties that make recorders work also give them their distinctive timbre.
Ubizmo
Recorder has a completely different fingering system than whistle (not to mention tone). Adding keywork to a whistle to make it more “chromatic” (it’s already chromatic to a certain extent) may or may not be a good idea but it doesn’t make it a recorder.