i'd agree - my guess is a dimmable MH
bulb would need a plate or something, to maintain an electron flow through the plasma, yet keep the energy level low enough to reduce light output
the other thing is the halides used in a metal halide bulb require a certain temperature to achieve efficient ionization, so, how does icecap intend to maintain proper ionization of all the different halides that are combined to make the desired color... some require a lot more energy than others.
thirdly, the hotter the arc, the less power required to maintain the arc, in what I'm sure is an exponential relationship, as temp increases, amperage decreases. so, dimming a bulb to 50% would require you to use 4x (or more) power to maintain the arc ... I'm sure that would work wonders for your electric bill, not to mention for feed circuits to the lighting.