To clear up any confusion, the dovetail is part of the cage and cannot be removed, but you can still mount any quick release you want. Check out the video for a closer look at the Varavon Armor Cage for the Panasonic GH3 / GH4 cameras.
There is an optional base with 15mm rails available at the website, but you could easily add the entire Varavon Cage to the top of any 15mm baseplate - as you would with a bare camera body. Here are some additional images, but for more information about the Varavon GH3 GH4 Armor Video Cage, check out their website (click here).
Varavon Armor Cage for Panasonic GH3 / GH4 Cameras