This is a winner, and the camera Canon users have been waiting for. 8K is a technicality. If it sports 40MP, IBIS, fully articulated screen, good ergonomics, great quality 4K, good slo-mo and two card slots, it will be hard to beat, particularly considering the quality of Canon R-mount lenses. A friend of mine bought an R and is very happy with the camera. This one will take him to heaven and beyond.
Heavy? Expensive? If it's anything like the R, it's about as heavy as other high end mirrorless cameras, and as for the price, it will probably be in the same $3-4,000 bracket as the competition has been for the last decade or so.
There are reasons why Canon have been market leaders for so long.