When Nintendo released their previous-gen console, the Wii U, they botched their marketing strategy almost catastrophically. The Wii U was, indeed, a completely new "next-gen" console in the Nintendo line, ie. in the same "console generation", ie. the 7th, as the PS4 and the Xbox One. It was not just a slightly fancier version of their previous-generation console, the Wii (which competed with the PS3 and the Xbox 360).
Nintendo botched the marketing because they didn't make it clear enough to the wider public that yes, this was indeed an entirely new console, a "next-gen" console, not just a slightly upgraded Wii. This has been estimated to be one of the reasons for the relative commercial failure of the Wii U. People were simply confused, as they thought that it was just some kind of Wii with an extra touch-based controller, or something. Many casual non-tech-savvy Wii owners didn't see the incentive of buying (what they perceived as) just another version of the same console.
Nintendo, perhaps having learned their lesson, did significantly better with the marketing of their next console, the Nintendo Switch. Massive advertisement campaigns quite cleverly made it quite clear that this is, indeed, an entire new console, the next "big one" from Nintendo. The real replacement for the old Wii.
Their marketing was so successful, in fact, that as far as I understand, the Switch broke the record of the fastest-selling console in its first week/month in history. If I remember correctly, the million units sold landmark was reached in just a few days, which is faster than any other console in history, including the PS4.
But regardless of this incredibly successful marketing campaign, it appears that Nintendo might be falling into their old habits.
The Switch was originally intended to be a merging of Nintendo's two major console lines, ie. the desktop consoles and the handheld consoles. The Switch was supposed to be, and is, a hybrid of the two, and can work as both, and thus ought to work as the next-gen replacement for both.
What that should mean, in turn, is that Nintendo's, and all third-party developers, focus ought to be concentrated on the Switch, with the Wii/Wii U and the 3DS being slowly phased out as the obsolete "last-gen" console pair. The Switch is now the next-gen console from Nintendo, for which all new games, in increasing numbers, will be made, handheld or otherwise. This was what many early Switch buyers were (and are) expecting.
But now Nintendo seems to be giving mixed signals about this, after all.
Some months ago there was a rumor that some Nintendo executive may have given hints that this might not, after all, be the end of the handheld 3DS line, and that there might be a "next-gen" version eventually, in parallel with the Switch. Of course this was just a rumor, and I don't know how reliable it was, nor have I heard of it since. Only time will tell.
Anyway, rumors aside, Nintendo just recently published a new version of the 3DS: The New Nintendo 2DS XL (that's a mouthful). This is essentially a New 3DS XL (which is a version of the New 3DS with larger screens, which in itself is an upgraded version of the 3DS) with a slimmer design and without the stereoscopic 3D effect. (The major advantage of it is, quite obviously, a somewhat cheaper price, compared to the New 3DS XL.)
In other words, a bit over three months after they published the Switch, they now published another version of the 3DS. This seems to signal that Nintendo is still intending to support the system for at least a few years to come, rather than having it end its natural lifespan as people move to the Switch.
Many critics, and Switch owners, are worried that this means that Nintendo is not, after all, dedicating all of their time, resources and effort on Switch development, but that it will still be shared with the 3DS line. It also might signal to 3rd-party developers to do the same.
Couple this with criticism from many major game developer companies that the Switch is not a very good platform to develop big modern triple-A titles for (because it's much less powerful than anticipated), and it only strengthens the reasons for the worries. Millions of people bought the Switch because they anticipated it being the next big thing. Will it, however, turn into just another Wii U in terms of a library of games and overall support?
Nintendo is giving very mixed signals here. I don't think they should, at this point.