I wouldn't worry about Canon. As per second quarter this year, they still dominated the ILC market with a worldwide market share of over 49%. Their little EOS M system also sells very well, and I believe it's still the most sold mirrorless system in Japan. They also have very deep pockets and full control over their value chain.
Nikon is in a much trickier situation, but I believe they have hit spot on with their new bodies. The Z6 is an advanced camera at exactly the right price point, and will be the perfect supplement to or replacement for the D750, which is still very popular.
Most people don't care about tiny differences in AF performance. People care about brand names and in protecting their investments. It's a Nikon and my old lenses will fit. Game over.
The only company that seems to be able to get around this is Fuji. Not that they didn't have a strong brand name, but Kodak had that too. However, with excellent cameras and lenses and even better marketing, they have made great inroads, particularly here in Asia. Notice that every time there's a new Fuji model, it's actually new, and it has significant new features. This as opposed to Sony, where most new releases seem to be focused on what was lacking on last year's model, the exception being the A9.
I think Fuji will sell more mirrorless bodies than Nikon, but I also think that DSLR cameras are here to stay, not until mirrorless cameras are better, but as long as cameras are sold as separate boxes that don't also include a communication device and a computer. Some people simply prefer an optical viewfinder. That gives Nikon (and Canon) and advantage.