Bitflipper, not only is it practical but it's pretty much main stream now. Except most on-stage guys don't use headphones they use in-ear monitors. Which is a fancy word for in-ear headphones!!
The difference is that the really good ones are custom molded to your ears. So if you see guys on stage with what looks like custom molded ear plugs, those are actually monitors.
Sennheiser, Shure, AKG, all those guys make the wireless monitor amps/systems. Just go to any music store or web site (musicianfri*, Guitar cent*, sweetwa*) all those guys and search for in ear monitors.
Basically 3 components to these things. A monitor amp piece that you feed your monitor mix to, which is the wireless transmitter. A belt clip receiver that each musician wears. Plug your in-ear monitors or headphones into the belt receiver.
Yep, they have all the same issues as other wireless gear. So you're fighting the same issues as wireless mics, wireless guitar/bass or whatever rigs. They all use the same wireless freqs.
But if you tweak with them you can get them to work well. Like with cell phones and other battery gadgets, the battery technology has gotten better so that's not as bad as it used to be. Still requires a bit of discipline to charge them correctly but workable.
gabo