I recently came across this interesting looking (potential) product on Kickstarter. It's a holster you wear on your belt on which you hang a couple of lenses. It's called the Quikdraw. Basically the lenses connect to hinged aluminum plates with standard bayonet mounts. You can remove the lens from your camera, attach it to an empty plate, grab another lens and remove it from the plate and attach it to your camera all with one hand. At this point, they only have designs on making these for Canon EOS and Nikon F mounts, but if it takes off it seems like it would be pretty simple for them to support other mounts (like :43 eventually. I'm not really sure I want to walk around with a bunch of lenses hanging off my belt, so I'll probably not order one, but this might be an interesting product for someone who's trying to shoot a wedding without an assistant or something of the like. Disclaimer: I have no connection to the designer/creators of this product and no stake in it's success. I just saw it and thought that perhaps someone else here would also find it interesting.