The price of the Z9 is really attractive. Nikon has taken a back seat for so long while giving up market share to both Canon and Sony that they pulled out all of the stops for this one. Sony took a similar position a few years back with the A9 vs 1 series in the pro-space. However appealing, I can't consider a system switch easily anymore like I used to when I was still shooting Canon lenses for cinema and Sony lenses for hybrid. Since moving 100% to Sony for both, with established workflows for everything from audio to stabilization and a ton of lenses, the Nikon is a non-starter for me, but I am quite envious of the specs and initial impressions and the $.The Z9 certainly makes the R3 seem considerably overpriced to me. I thought it was overpriced when introduced but placed an order anyway. My only real disappointment with the R3 at introduction was the 24 MP. I really wanted 45 MP and hesitated for three hours opening day to place an order, so likely will not be receiving it in the first batch.
Even before the Z9 introduction I was waffling on the R3. This weekend I will probably make up my mind whether to cancel the R3 and place an order for an Z9 and Z7ii and some starter lenses and begin selling off some of my Canon lenses. With the fully electronic shutter, what appears to be even a more sophisticated AF system, equivalent handling (although a bit different) and frankly a better back LCD for a wildlife-landscape photographer and the 45MP, the Z9 simply appears to be a better camera for less money.
The question remains about some important lenses. The 400/2.8 + 1.4x looks great but how heavy? The 100-400 looks great and is certainly light and compact enough, but optically how good? Canon's 100-400 ii and 100-500 are superb and the best lenses per dollar I have ever had. Can the Nikon match that? They could not with the old F mount lens. I very much like my 24-105/4 RF lens and use it for landscapes without hesitation as I did the 24-70/4 L IS before it. The old F mount 24-120 was a decent lens but not up to D850 standards.
Encouraging about a switch is many if not most of the Nikon S lenses have been superb and in some cases preferable, at least optically, over Canon RF lenses. Examples are the 24-70/2.8 and 70-200/2.8 and the 14-24/2.8. That said, we are talking pixel peeping and not real world usage in the field making real prints to sell for someone's wall.