BTW, why call it 4/3 cameras?
Dimensions of the sensor, just as Canon/Nikon and everyone else is a 3/2 dimension. Has nothing to do with the physical size, just the dimensions. Panasonic cameras accept Olympus E series lenses, just as Olympus E series camera will accept any lens that happens to come along from Panasonic to fit their cameras.
Beware using such super zooms made for 35mm cameras. They are very slow at the long end- typically f5.6, making the already somewhat darker viewfinder of a camera like the L-1 even darker, and there are no physical focusing aids on the viewfinder screen, making accurate focus difficult, but there are some good adapters out there on eBay that allow you to use many types of manual focus lenses on 4/3rd cameras, both Olympus and this new L-1. I've been considering it myself, but to use with a little better, fasterset of optics, like a 180/2.8 Nikkor or maybe I can hunt down a manual focus 300mm f2.8 Nikkor- decent examples today of that lenscan be found for under $1,000.