Hi Meir,
You said it very well. The Boehm system evolved due to the need for orchestral instruments to be able to play in any key. As you pointed out, there are tradeoffs in order to be able to do that. Simple system flutes and UPs play well in their designated keys and in Irish music we need the flexability of the open holes for effects we can only get from them. Like the tin whistle, if you want to play in C, get a C whistle or C set of UP. Same goes for many other keys. The Albert system clarinet survives for the same reasons. Greek and Klezmer music makes use of this same flexability which is not possible with a Boehm system clarinet.
Hope your piping is progressing nicely.
Regards,
Ted
Ston,
The UP evolved when there were few keys on oboes etc.. The register key never made it to the UP. It certainly is not modern and some research is presently being done with a register key on a UP chanter to facilitate the upper second octave. I don't see much need for the third octave but Tim Britton gets a few notes into the third octave on his sets. As has been pointed out, without embochure control on the reed, the third octave sounds awful rather than musical. You might as well have a pipe organ for the fipple voice, and extended range etc.. A small portative organ with a foot bellows perhaps...
Ted