Something I recently made over the holidays.
The Multiwhistle is the work of 3D printing. It is made as one piece not four fipples glued.
Four ABS co-joined high whistle fipples side-by-side each with a CPVC tonebody in the keys of C, D, Eb and E.
Good when you need to modulate or switch keys quickly.
This needs a youtube demo! 
Nifty. You can play panflute style, too. The next one you make, you should have the keys going from the high G down to a Bb. That would give you some serious range. With the ABS plastic, it won’t be too heavy. Would love to know how these sound, too.
Assuming this is a joke because one’s fingers are never going to be comfortable reaching across the way this thing’s going to require from one hand or the other?
If I need to switch (whistle) keys quickly, I’ll put one down and pick another up!
That’s my thought as well.
But Daniel is pretty handy with keys on whistles — maybe a single set of touch plates could control four sets of keys. No shifting of the hands or fingers!
You could play that whistle along with one of these
Maybe closer to Rahsaan Roland Kirk?
https://www.google.co.uk/search?q=rahsaan+roland+kirk&tbm=isch
It’s designed as four whistles because an average person can reach over four, but not five or more.