DPReview is the single best online resource for in-depth camera information and reviews. Well written, concise, and trust worthy. Of course they aren't written from the point of view of an underwater shooter, but it's still a fantastic place to read more about any given camera.
The GH5 was recently announced and it's every bits as awesome as people had hoped. Bang for buck the GH5 could be one of the most important camera system for underwater videographers: a small, broadcast quality, and affordable video system.
Though the camera is not yet out (pre-orders are being taken) DPReview have posted their first review, and it's well worth a read...