How about more efficient electronics that can power the device for much longer between charges? That would be very sweet.
I've mentioned earlier some of the other "practical" and cosmetic things I would mind seeing -- but if the internals had a broader range for some of the higher wattage vapers AND was more efficient. WOW.
From what I've read, the ProVari is one of (if not THE) most efficient regulated vaping device out there. Depending on how clean the threads and contacts are, it is 90-95% efficient. Only 5-10% of the battery's energy is wasted.
How old are your batteries? And what brand of battery are you using?