The RX100 series is excellent, at my dive club several divers use them in underwater enclosures. The thing with the RX100 IV is, are you going to spend 1K if for the same money you can have a mirrorless Sony A 6300, which is vastly superior at absolutely everything, you can pick and choose lenses, and is still a very compact camera. Unless the utmost pocketability is the most important thing for you, I'd check the A6300 (amazing 4k video, 120FPS FullHD video, magnesium weatherproof body, mic jack) at 1K, or if you can do without the 4k quality and SLog profiles, mic jack, etc, the A6000 for about 500 bucks.
Any reviews over on
www.dpreview.com will help you out with the details.