I wouldn’t see that as a bad thing. You still have whistle voicing, and the characteristic whistle fingering, with another option to make the instrument more flexible and expressive. I’d be interested to see what you come up with. It could be a killer instrument.
Ah, this is exactly the kind of information I have been searching for. Thank you friends, for the replies and suggestions. @Pancelticpiper: Big fan of your YouTube videos. Nice to make the connection online.
Sounds like I need to raid a whistle shop and try these out for myself. Since I already play the flute, I find I am more interested in whistles with a sound separate from a flute. More exotic, more traditional. “Chiffy” (or “dalefulness”–@Dale) appeals to me.
To make a true vent hole that serves the high B and C, I think you’d have to put it even higher up on the tube.
I only have one cylindrical recorder (a Bleazey session soprano) and the vent hole plays a perfect second octave D. Tapered bore instruments need it higher up, I think, but most whistles are cylindrical.
Edit: I was wrong - it turns out to be about a quarter tone higher than the D. Apologies - I wrote the original message when I started work early this morning and didn’t want to disturb my daughter by playing the recorder straight away.
But- since the position of the hole is a function of its size, as I understand it, the amount to which it is pinched will probably be more critical than the absolute position on the tube. You do change the pinched aperture to fine tune the highest notes on the recorder (yes, fussy recorder trick, I know).
daleishness
daleicity
dalehood
dalehoodedness
Yes, the D fingering on a C recorder is O|XOO|OOOO
But for a D whistle I think O|OOO|OOO would be better,
for easier C#-D transitions.
So I would tune the thumb hole to D, with all fingers off.
0|0X0|000
But maybe this should go offlist?
I will start a new topic after I’ve done some practical research
and have something to report on this matter.
I’ve got enough info to get me going.
The “Dirty Dale Effect” - or, DDE for short, maybe?
Now you’re on to something. That’s jazzy, and slightly dirty… but then I am from Las Vegas. 
I’d prefer “Dirty Dale Distortion.” There’s something about the DDD label that makes me feel all warm and fuzzy.
Yeah, plus I doubt Eisenhower would have been too thrilled… 
hehe. Imagine what non-whistlers would hear: “My such-and-such low D has a lovely round DDD, fuller and more responsive than such-and-such.”
Ya’ll would sound like producers of adult movies. 
What? With this haircut? 