So it's hard for me to say definitively, because I haven't run the 1000 iterations of LEDs out there. LEDs keep getting better and better—I don't think it will be long before LED replacements are kind of a default. I suppose it's possible that someone has created a bulb that works with the housings, but I haven't seen it yet and it kind of sounds like neither has anyone else. @C6H12O6 has good information—I did that for a while, and it was a good improvement.
I gave up looking—HID and no need to look back. The best-of-the-best LEDs are hardly comparable. It was expensive, but the results are nothing short of ridiculous. Mine is an LX—worst factory beams I've ever owned. Maybe the LCs have better stock beams.
No you are correct, technology is advancing fast enough that yes, we are getting to that point where the PCB that is holding the diodes is getting thin enough to create the same "thickness" of the halogen filament. Can't remember which one, either TheRetroFitSource or Headlight Revolution, but one of them did a really good video on explaining all of this. Think of it like having one of those
harbor freight led flashlights that had the
zoom telescoping front to allow you to focus the beam. When you have it pushed all the way in, the beam is not really focus, light is thrown all over the place and while there is still a
hot spot for the main portion of the beam, really there is light spill everywhere that you have no control over. You can focus it in and out to help centralize the hot spot, but really you will always have spill.
With many cheaper bulbs and setups, that spill is what ends up blinding oncoming traffic because there is just light being thrown all over the place, and you as the driver really don't have a clear vision of the road. Flipping on the hi-beams only compounds the issue and makes things worse. So unless you really are ready to make the jump to an expensive LED bulb (like Diode Dynamics, Morimoto, or GTR) then stick with a good, quality halogen bulb. Those three companies do make
compatible solutions for reflector housings but they even preface it that while they will work OK with those housings, for optimal light output and focus you want a specific LED/HID projector housing. Oh and all of those, you are looking at right around the $150 mark starting out for just one set of bulbs.