We've had second hand MV lights in our shop for some time... about two years ago we bought a couple of the fluorescent screw-in bulbs for a couple of them (as they died). We did have to strip the guts of the fixture - remove ballast etc, and direct wire the 120 to the bulb, as I believe the bulb had its own integrated ballast. They are really nice; in the cold the come on instantly, though not full brightness; and they don't seem to mind being turned off then on in quick succession like the MVs do. While the bulbs might be a little more than the MVs, there are "less" parts to die - I forget the brand, but I think they were in the neighborhood of $100; but a nice way to recycle the fixture.

Dave

Another interesting question is, what did light fixtures look like in the 1920s, 1930s, 1940s... and what would it take to emulate that look, but in LED?

Some manufacturers offer retrofit kits for some of their products, for example Sentry Lighting. U.C. Berkeley has converted lots of Sentry's "Tulip" fixtures on campus:
http://www.sentrylighting.com/led-led-retrofit-108-108-142.html

I think that there would be a business opportunity for generic retrofit kits consisting of an LED array with an Edison (or Mogul) screw base and an omnidirectional pattern, and a driver module which could be installed in place of a ballast and would work on common voltages (110, 277, etc.). (By "omnidirectional" I mean circular perpendicular to the bulb's base but not necessarily emitting anything "upward" from the base.) A lot of existing fixtures have built-in reflectors which are still usable.