Even if LED's catch up in lumens/watts, we still have to consider what kind of throw they can produce from a given diameter housing. HID's have an advantage here, since the light they produce originates from a very small point, vs. the large emission area of high power LED's. This translates to a tighter beam from a given diameter reflector.
I think LED's could displace HID in short-range/flood applications pretty quickly. That's all about efficiency. On the other hand I'm not aware of many such HID applications - automobile low beams, maybe? :thinking:
Long throw applications, on the other hand, will require advances in both efficiency AND in optics design. My guess is that we'll see HID around in the long-throw niche for several more years.
Regards,
Bob