I'm very interested in this as I am definitely upgrading my Hero4 before my Philippines trip next March. Based on side by side comparisons, I had already decided to get the Sony FDR-X3000 over the Hero5. I have been waiting to see if Hero6 changes the game.
The Sony is cheaper, $368 on Amazon and includes the housing rated for 100m.
The Sony has optical image stabilization which seems to work very well in videos I've seen.
The Sony has better color than the Hero5 but we'll see how the Hero6 does.
The Sony does not have a back lcd screen, a definitive drawback. On the other hand, I've struggled to see well in the Hero4 lcd. I can sometimes tell if the lighting is off or if the subject is centered though so it's still useful. But I could always mount the Sony and my old Hero4 on the tray and use the Hero4 lcd for that.
Then again, who knows what new model may come out in a few months?