I investigated addng HID lights to my daily driver Nissan Altima. There are a ton of kits avaiable at all kind of price ranges. As stated earlier, the temp range does dictate the type of light thrown. What I found was there were big compromises in putting HID bulbs in a housing desingned for a regular bulb. And reliability was all over the map, depending the the kit you bought. So, I passed.
I would assume these compromises would also be present in a bike headlight. Unless you replace the whole unit like the Kuryayn kits for HD's work. Possibly one of the Kury kits for an H-D would work in our bikes? How many headlight sizes can there be?