I once replaced a couple of QR front axles with solid axles from Wheels Manufacturing. Watch out that there are hubs with both 26 threads per inch, and 1-mm threads, hard to distinguish. These were cup 'n' cone bearings.

Necessary? Useful? Don't know.

When I got my first bike with QR hubs, my dad said: "Watch out that some joker doesn't flip those levers while you've parked your bike somewhere." Those words have always stuck with me for some reason.