Since I don't have a Z8 to play with, my comments are from the z9 only.
I'm not sure I'd use this option for my use cases. It's pretty rare I'd have to swap between disparate options that aren't already on function buttons (eg single point to get through brush, and the hand off options that don't carry through when cycling based on your comments). The times I manually change af mode are when I'm going to set up for something specific with a custom area (wide and short above grass, or tall and thin to poke through it) as the default, and cycling through I don't think would be any faster? Maybe a bit, but I usually have time to swap.
Can you elaborate on why you feel it's a game changer?
Mostly because I'm not pressing an additional button the entire time - that, and changing AF areas is almost instant.
For example, let's say you have 3D as an override on the Fn1 button and your primary AF area is Wide AF. If you get into a situation where 3D makes more sense, it's tempting to just push and hold the Fn1 button for the duration - I know because I see people do it all the time
Heck I do it all the time instead of changing AF areas
Instead, if I see I need 3D for more than a moment, a quick press or two on my video record button puts me there in less than a second. Much more convenient than messing with the press-and-turn setup we had before.
The thing is, as Nikon shooters we have become accustomed to having AF areas scattered all over the camera on different buttons we have to continually press to use. I've always found that I'm much happier if I'm just in the proper AF mode without the extra presses. This makes switching AF modes very nearly as fast as overriding them.
However, this isn't a replacement for those overrides with action. There are still times I may be using Wide AF to get on a specific target and then want to handoff to Auto, for instance mid-flight. This doesn't do that
Where this shines is that it makes it much faster to jump to the proper AF area as needed. One of the major reasons for focus problems is using the wrong AF area. In the heat of the moment, it's tough to get yourself to switch to a better AF area - at least it is for most. AF overrides work, but if the best AF area for the job isn't on an override, it's tough to take the time to switch for fear of missing the shot. Once you get used to cycling (we call it toggling in the Sony world), it really makes a difference. At least it did for me. It's all about making the camera faster to use.
Also, this isn't just speculation on my part
I've been using this with Sony for three years now and although ti sounds minor, it's made a big difference for the way I shoot.
All that said, everyone is different (just ask if BBAF is better than shutter AF LOL) so use what works for you.