I have a couple of HiD lights for my HP2 (front and aux light).
But I think if I was you I'd wait a few months and see what happens with LED lighting availability as an aftermarket option for BMW bikes.
The GS1200 2013 has an LED headlight as well as integrated LED auxillary lights: unless I'm misunderstanding the press release package that just came out.
And maybe someone like Touratech and Wunderlich and others in the USA will start to bring out LED headlights for bikes.
Is a HUGE market: I bet a very big percentage of GS1200 owners would buy one if they could.
Doesn't burn out, less power, more powerful than std light.
Even if not, I'd look at LED sidelights: are really good now and less power drain. You might not need a brighter headlight with them.
An HiD can be a bit of a headache: not just wiring it up, but you can get hassle from MOT, and there's a few other issues.
So if I were you I'd hang ten on HiD's.
Maybe buy LED aux lights in the meantime then in 6 months or so can buy an LED headlamp kit.