Peter, have you surveyed many other users about whether those features are essential?
I personally don't feel the tail switch is essential. I think it makes the current Arc LS too big. If I buy an Arc LS then I'll certainly get the twist cap for it. I have to say the LS is a nice light but my interest in it dropped considerably when I saw the thread about Larry's light. Larry's is the small 123 that I lust after now. And the bigger and fancier 123 light that I keep drooling over is the McLux. I have to say that compared to those other two, it's the LS that's both too big and too small. Of course I love my Arc AAA I'm eager to see the LS4.
Larry made an even smaller light using a CR2 cell. A commercial one would have to run at reduced power to avoid overheating, but would still be impressive (like a Micro Illuminator).
Of course no light is ever small enough, but the Arc AAA is not at all bothersome on a keychain if you have more than 5 or so keys. Larry's CR2 light is noticably shorter (though thicker) than the AAA. Perhaps it could work out better on a keychain than the 123 version.
Here's Larry's "family picture" (Arc LS, Larry's 123 light, Larry's CR2 light, Arc AAA, Arc AAA with N cell tailpack, Leatherman Micra). I want one of each!!! /ubbthreads/images/graemlins/smile.gif