My thing about the Switch is that the dock means Nintendo doesn't actually have to release a full-blown new system for a while.
They can just make incremental upgrades that run more advanced games or at least, less compromised versions of third party games. And run first party Nintendo games at increased resolutions and frame rates. Making upgraded systems with the Tegra X2, maybe even NVIDIA Xavier, and any other similar GPUs down the line, would be pretty easy for them to do, along with CPU and RAM upgrades.
The fact of the matter is that the Switch releasing as a mid-gen console (and closer to the launch of Sony and Microsoft's next systems than the release of the current ones) puts it in an awkward position if Nintendo waits until they come up with a full on new system with the next big idea. Third party games are going to want to take full advantage of the new systems and it will become increasingly harder for them to make low-end Switch ports.
However, if Nintendo treats the Switch like the iPhone and makes a new upgraded version every 2 years or so, they could keep up with the latest third party games without having to reinvent the wheel. They can also upgrade the OS while they're at it.
This wasn't a major option for them in the past because Nintendo used very outdated architecture. They used PowerPC right up until the Wii U, which was the main thing preventing many third party ports when other consoles moved to x86. The Switch doesn't use x86, but it does use NVIDIA's ARM architecture which is still more modernised and easier to develop for than PowerPC. Plus, having NVIDIA working with them makes it easier for Nintendo to just commission these needed upgrades.
I honestly think they'd be silly to stick to the old way of releasing their consoles because it isn't a necessity anymore.
The dock's role in all of this is that they can sell variants without the dock, making the upgrade transition easier for owners of past Switch models.
It took 15 months for a second DS model to appear and no one gave a **** about it.
That's because the DS Lite was just an aesthetic revision, it didn't change the specs.
And FYI it still sold like hotcakes.