For the price, no other mirrorless camera offers so many features than the new Panasonic DC-GH5. If there is anything you want or need to know, I suggest tuning in to the LiveStream Panel event with B&H. The embedded video will be live today, March 29th.
As someone who has been shooting with the Panasonic GH4 for years, there's plenty of reasons to upgrade to the new GH5. For myself, the features i'm looking forward to are the wider field of view in 4K video mode. The GH4 would crop in tighter and in order to shoot wide, I would always have to switch back to 1080. I'd also have to drop down to 1080 whenever shooting 60p, but now the Panasonic GH5 offers 4K/60p internal recording. The in-body image stabilization is going to make handheld work with my manual lenses much easier, and the GH5 will also provide much more professional Audio inputs with the (optional) adapter. See the new Panasonic GH5 over at B&H (here).