I was trying to think of other stuff, and I got to thinking, what is the primary design influence when building a typical hotwire? The mag it's built on, what else? So I suggest that if we're looking for additional ways to improve hotwires or try new things, lets try addressing the problems that come with the host light - as a result, these parts/changes would impact a wide variety of mag mods, not just ones with a certain battery configuration. For the sake of brainstorming, I'm going to list off some things that I feel are candidates for improvement in a basic mag with no regard for what has been already addressed with mods or offerings. This is a brainstorm only.
1) As already mentioned, the stock switch stinks. It has high resistance and it doesn't handle heat well. It also takes up too much space so mods are bigger than their battery configurations dictate. Ditch the side-switch for a twisty or tailcap switch, or make a shorter side-switch. (Hotdrivers/regulators excepted, of course)
2) Tailspring stinks. It also has high resistance and takes up too much space. It also sits higher in the tailcap than needed, taking up more space. Make a few different-length low-resistance springs available with tailcaps modded to hold them at the bottom where they belong.
3) Stock reflector stinks. It melts and it doesn't reflect well. Continue manufacturing MOP, but please make SMO and LOP too. Continue with throw-head design with an eye toward cost. Might be nice to have a throw-reflector that fit in the regular head.
4) Stock lens stinks. It melts, scratches, and has lousy transmissive qualities. UCL and Borofloat lenses are much better. Might be nice to get a sapphire lens too.
5) Alkaline batteries...well... stink. The FM battery holders are the standard by which all other battery holders are judged and I love mine. In order to boost sales and improve usability, I suggest continuing with the 6xAA/6x14500/9xAA/9x14500 holders (remember people like building ROPs!) unless the C and D li-ions decrease demand below acceptable levels, but make a complete charger-solution available through you, or at least offer the male charging jack pre-attached to wires with a standard connector on the other end. Just buy the charger, connect the jack adaptor, and plug in.
6) No lanyard attachment point. 'Nuff said.
7) Security/police types like cradle chargers. Might be hard... but then again, it sounds like you might be bored and are looking for ideas...
Last, not a gripe about the mag but an observation:
8) All of this stuff is spread out and its hard to know what's available (I know I've been surprised when I've seen some threads linked to in a discussion). A stickied master-thread of all FM sales threads would make things a lot easier, especially if it also listed smaller items you carry that could be appended to a primary-item order. That would save you from having to update a million different threads if you ran out of Boro lenses, for instance, and it might increase orders of those items with primary items. Finally, I know my mind has an easier time playing with Legos if all the pieces are in front of me - it seems to be the same with flashlights. If all the available parts are presented in one place, I think more people would end up with the hotwire light(s) that they will be happiest with.