They changed the design due to the new circuitry, but that redesign included 4K output, freeing up USB 3.0 lanes on the USB-C/DP connector, and includes two models already. It was also only 2 years ago, not even that at present. Nintendo designs peripherals to last, literally. Nintendo Wi-Fi Adaptor AC Adaptor spanned three families of devices and two generations, Wii AV cables spanned two generations, NES AV and AC Adaptors spanned two generations, DMG 4 Player Multitap survived three redesigns and a new generation where it remained relevant to play BC games in 4 player mode.
If the shoe fits, the shoe gets worn. The GBA AC adaptor worked on DS, and so, it was used on DS, and so on, and so forth.
The dock is just that, it's a DMG 4 Player Adaptor, it's an AC Adaptor, it's AV equipment, it's all of this in one unit, and the Nintendo Switch Dock with LAN Port (which, somewhat oddly, doesn't use the term "Nintendo Switch Dock (OLED Model)") has more than enough technical specifications to handle the next generation of Nintendo devices, at least for now. From its increased ventilation to enhanced output abilities, and let's not forget much more forgiving tolerances, to the point even a thicker device could fit, nothing indicates that it was just the 2 year gap filler one might think it would be. Pennies. Matter. In quantities of a million. And in quantities of a hundred million, even more. Simplifying production going into a new generation by going from two docks and two sets of HDMI cables to just one that works across the entire range means huge savings, and all that wasted plastic making the ins and outs of the ventilation system on the Dock with LAN Port were hardly made for no reason; no existing Switch can come close to overheating in the Dock with LAN Port. Why is the best ventilated dock the one that comes with the most power efficient model?
Well, probably because it's also going to come with the most power hungry model.
Also, they have been VERY particular with the marketing, only ever marketing the White Nintendo Switch OLED Model and its White Dock with LAN Port. Nintendo Switch Dock with LAN Port (Black) has been broadly absent from advertisements, so the visual identity going into the next generation would be very very clear; white Joy-Con, white Dock, rounded design is the old Switch. Black dock, black/dark grey Joy-Con and a redesigned body is the new Switch. Nothing stops them from reusing it in advertising because it already has the capability to provide a unique identity in marketing. Did Sony really stress out that say, PS4 Slim and Pro shared so many design elements? Same idea.
Unless they want to push this thing to HDMI 2.1, which I see few benefits and a few caveats in even trying to do so, 2.0b will be fine, it even allows games to target 1440p120 if they want, because as impressive as this device is, 4K120 it is not.
Not to rehash myself too much, but there's also just plain consumer goodwill to keep in mind! Even Microsoft knows that, and kept controllers, cables, even power cables and HDMI cables, game drives and so forth, cross compatible across five models and two generations of Xbox and everyone loves them for it. When Nintendo is making a new console that must by means of its market position as a hybrid, observe the same formfactor as its forefather, it is such an easy win to ensure devices are compatible so we don't have to go out and buy all new Pro-Controllers and Joy-Con. Optional improved controllers? Sure, I'm game, that's what Xbox did and nobody complained, the Xbox Wireless Controller (2020) (Yes that's its official name.) is excellent, my favourite controller ever excluding those with gyro.