Just got a Canon G3X, which is waay down the scale in prestige, but Michael has a review of it on this site, and on the strength of that I got one. First out of the box yesterday - looks promising. I took a handheld of a squirrel on my roof at equiv 600mm and it looks promising.
I will put it on a gimbel/tripod setup and see for sure, but it does look promising.
I owned a Nikon 500mm some years ago and have had long Canon lenses, so this camera is like a toy in comparison.
Unless you are going to sell prints etc, this thing is quite interesting.