Fengniao had a chat with a bunch of Panasonic managers. An interesting story is this one:
At first, we also simulated the GH6 without a fan, and found that for the GH6 to be cooled by natural air as before, it needs to have a larger surface area for heat dissipation than the S1H. Therefore, we chose to install an external cooling fan, and after repeated thermal analysis simulations, we were able to guarantee both cooling efficiency and compact appearance.