I took the survey, but I'll follow the lead of others who have taken the opportunity to express their views on this thread...
Type 3 HA is very important for a keychain light, because of the constant abuse inflicted by keys, coins, and other pocket contents.
Small size is extremely important. A CR2 sized light would be the upper limit of what I consider to be a truly keychain sized light. While I really like the looks of the KeyLux-AA, I'm passing on purchasing one because I don't think I'd actually put it on my keychain (I found the Arc AA to be bit too large for comfortable keychain use). I'll use the funds to buy an extra KeyLux-N when they become available again...
At the current levels utilized by keychain lights, is there really much difference in output between a Luxeon 1 and Luxeon 3? I've read that tint quality is generally better with the Luxeon 3s, so that would seem to be the main factor, as opposed to output.
I like the concept of a head that can be used with AAA or N cell bodies, at the user's discretion.
Variable output would be extremely useful - at least two stages. A low level of light would provide the option of extended runtime. The output of a typical 5mm LED is still plenty of light for performing most tasks in total darkness.
While I appreciate the utility of a light that uses common batteries (AAA or AA), I would be willing to use an uncommon battery if it meant a significant decrease in size, or a significant increase in brightness and/or runtime. Case in point: the NiMH N cells for the KeyLux-N. I think a light that used a li-ion CR2, N, or AAA battery would be fantastic. There might be some resistance to abandoning common batteries in favor of an exotic, "proprietary" power source, but TnC lights are for discriminating flashaholics, not the mass market. Maybe the regulation circuit could be tweaked so that the light could be powered by alkaline/NiMH/lithium batteries in an emergency, at the cost of decreased output?
Anyway, that would be my "dream light".