According to the latest rumors from the 43rumors, the upcoming Panasonic GH5 will have the same size as the Panasonic GH4. This means all the current Panasonic GH4 cages will also fit on the new Panasonic GH5.
Panasonic GH5 is already listed at at B&H! However, there is no info about pricing and shipment date.
See also 2016 Black Friday & Cyber Monday Panasonic Camera Deals