With the GX8, you can work outside in bad weather, with the correct lenses. You could try to do that with the GX85, for a shorter length of time, of course, before it malfunctioned. Weather-sealing is a big advantage for me.
For me? The most important is that the IBIS works for 4K video. Gx8 doesn't. Finally what I always wanted. The Stabilization equivalent to oly's, but video using Panny's superior codec and with 4 k as well! Only down side is no ext mic input! But that can be worked around.