Why?
Power density - a CR123 based light will either give you a lot MORE light for the same size, or be smaller.

That said, I think the best light for disaster use are "dual battery" - My old ARC LS came with both a CR123 tailpack, and a 2xAA tailpack - I understand that the EDC ultimate now has a AA tailpack, but as funds are REAL tight right now, I have not looked into this

I know I can get a LOT of hours on my CR123 based ultimate - simply by NOT using the highest setting. I think I've changed the batteries 2x in the year I've had it