Absolutely yes.
What's better than 9V rechargable? 12V rechargable!
A single CR123 length (18330) would be good, and could be modular, but the option of a full 18650 extender would be fantastic. Not to mention that you would be just about the only person offering such a product!
You better be careful there Leef, keep going like this and Surefire might just start losing customers completely to you... keep up the good work!
(keeping my eyes peeled for the standard bezel and turbohead...
)