The UK price will hopefully be around the same price when the GH4 arrived just under two years ago…£1550 – £1700. Remember although it has an impressive 10bit 422 colour space this will not be available in 4K 50p mode. I bought the 12-60 lens with my GH4R and its a great lens apart from the f3.5-5.6 aperture, this was a major disappointment after the f2.8 constant aperture 12-35mm lens. No info on a dual card slot, but with Olympus at their heals hopefully Panasonic have added a dual card slot.
The Olympus OM-D E-M1 Mk11 (£1,849) has a dual card slot, 4K and a very good stabiliser plus a headphone and mic socket. I have 5 Olympus lenses (3 Pro) and they are the best money can buy.