Nintendo have had account systems in place since the launch of the Wii U in 2012. The Nintendo Network ID tracked purchase history across both Wii U and 3DS, had a shared wallet, and a handful of games even
supported cross-buy across the two platforms. If I recall correctly you could also make purchases through a web browser and they would automatically download to your Wii U or 3DS.
For a variety of reasons, the lack of BC with either Wii U or 3DS being the major one, they transitioned to the Nintendo Account system instead with the Switch (although you could link your NNID to your Nintendo Account, I'm not sure if it did much).
This is why I think the references to building long-term relationships via the Nintendo Account are notable. They could have said the same thing about Nintendo Network IDs during the Wii U/3DS era, but they didn't. The Switch was a hard reset for Nintendo in terms of their hardware architecture, and they took the opportunity to also reset their account system, but the intent both for the Switch hardware and the Nintendo Account always seems to have been to facilitate forward compatibility with future systems.
The constant references to the Nintendo Account in these presentations are Nintendo's way of telling investors they're not going to have to do another hard reset, because they've planned for a smooth transition to the Switch 2 since they started working on the Switch. And although they obviously can't talk about the hardware part of that before they've announced the new console, they're absolutely going to take every opportunity to talk about the account side of things.