Back from the dead! I want one as well! I'm not interested in getting a third set of batteries, maybe I'm the odd duck, but I want the compactness, OR battery life of the 18650. I ordered a mini because I like the form factor of my BB when I'm out and about, I'll sacrifice battery life for that. But I can see times that having an 18650 would be a benefit, certainly on road trips etc. I don't see this as killing the regular Provari sales, many want the normal size, many want the ability to expand. The 18650 ext. gives the option to be everything, to everyone that wants the smaller form factor, and battery life!
But I don't think it will ever happen, so I hope I am lucky enough to get the Kir Frans extension while they are still available!