Well, time for a revisit since I've had both low beam globes blow two weeks apart last month: first the left and then the right. In the process of replacing them, I kept the old ones and now have what could be, with glass and filament removed, bases for building up LED equivalents.
And yet, the commercially available ones come with heatsink/fan arrangements, so even if I source the CREEs and add my old CPU fan and heatsink components, it won't be economically viable or as tailored to the application.
Sad how electronics is increasingly less DIY and more throwaway.