HID bulbs should not be used in housings designed for normal incandescent bulbs. The extra light produced causes the reflectors to become overloaded, and light is scattered in a way which is not the same as with normal bulbs. Youll basicly dazzle people coming the other way. Projector lights might be different mind you, not too sure about those.
With your hi/lo beam question. Some h4 kits ive seen have a rotating reflector on them which allows the switch between hi and lo beam. Some have two capsules, but you lose the ability to do a quick flash due to the warm up period. Having a design that uses two bulbs and one ballast would still suffer from the warm up period delay when switching between bulbs, so that wouldnt help either.
Ive never seen different colour temperatures used in the same bulb housing.
Basicly, unless you have a single HID capsule (with a rotating reflector that moves damn fast) that can act as both a hi and lo beam, and you want an HID hi beam, then you will lose the ability to do a quick flash.