There is no “update” path between 1.x and 2.x, to the point that we intentionally publish them as different image names so you can’t accidentally end up on 2.x or think it is a newer version of the same thing.
So TBH I have no idea what your point is really, what the software “let [you]” do, how we could prevent that, or what you think should be added to the documentation.
If it’s basically a “Should I just keep using 1.6?” section of the 2.x docs, that’s not going to happen. Nobody should do that. Support extends out a year and a half or so to give customers time to migrate, but the large majority of development is on 2.x and we’re certainly not going to encourage new installs of 1.x or sticking to it indefinitely.
I think the website is pretty clear on what the current product is, starting from the first sentence:
Multi-Cluster Kubernetes Management
Rancher is open-source software for delivering Kubernetes-as-a-Service.
It’s an entirely different product, it appeals to an overlapping but different set of people, but this is the way the market has been heading for a while. K8s is powerful but not friendly or easy to use, so we are working on separate projects to bring a simpler experience on top of it for later this year.