The new Panasonic S1 full-frame mirrorless camera is now shipping and it is already in stock in WEX UK and Park Camera:
In the US the Panasonic S1 is scheduled to start shipping on April 4th: see the listings at Adorama and B&H. The Lumix S lenses are also expected on April 4th: Adorama | B&H | Park Cameras | WEX.
Panasonic currently has a limited time offer: if you pre-order now, you can get a free Panasonic DMW-BLJ31 battery and Panasonic DMW-BGS1 battery grip ($435.98 value). See the details at Adorama and B&H: