Summing up my thoughts for the whole thing, I think Nintendo's strategy for the 3DS is a good thing. As the 3DS is winding down and the Switch is ramping up, we've seen Nintendo make statements on their continued commitment to the 3DS and its owners through 2018 and (maybe) beyond. I'll even double down and say it's the best thing. Too many times we've seen Nintendo drop a platform like a bad habit as soon as something newer is available. But what Nintendo should have done with their aged systems for the past few generations is what they are finally doing with the 3DS. And that's basically to treat it as their PS2.
Keep in mind that from what we know about the current projects of internal Nintendo development teams, they have
zero projects currently in full production. Every one that we know about has either already released a Switch game or is making one right now. Reposting from a couple pages back, here's a list of currently announced 3DS games:
Kirby's Blowout Blast - HAL
Hey! Pikmin - Azrest
Miitopia - Nintendo
Culdcept Revolt - NIS
Metroid: Samus Returns - MercurySteam
Layton's Mystery Journey - Level-5
Etrian Odyssey V - Atlus
Monster Hunter Stories - Capcom
Sushi Striker: Way of the Sushido - indieszero
Pokemon Ultra Sun/Moon - GameFreak
Radiant Historia: Perfect Chronology - Atlus
Shin Megami Tensei: Strange Journey Redux - Atlus
Of all of those games, Nintendo is listed as the developer on only Miitopia. It releases in NA/EU next month. Even that is a late port though. It launched last year in Japan. Its development team, presumably, has also moved on to the Switch. I think it's the best thing for satisfying as many of their fans as possible. EPD and other internal teams like Retro and Monolith are all busy on creating new content for the Switch, just as everyone wants them to be.
That leaves a handful of producers to work with external teams on keeping the huge built-in 3DS audience satisfied. This applies to Pikmin, Kirby, Metroid, and Pokemon. With many of these external teams, we know that they decide their own projects and platforms. For example, we know that GameFreak does whatever the hell GameFreak wants and they're no strangers to making Pokemon games for platforms that already have a successor. We know that MercurySteam pitched the idea of a Metroid 2 remake for 3DS to Nintendo in 2015. What these partners decide to do with their resources is, rightfully, on them. It doesn't put much extra on Nintendo's plate to assign a few employees in producer roles for these games.
The rest of the support for 3DS is coming from 3rd parties, companies that don't have a new piece of hardware to sell. It is absolutely in Nintendo's best interest to push new hardware and cultivate a new audience on that new platform. For 3rd parties though, the goal is to reach as many players as possible. That's why Atlus and Capcom are putting their games on PS4 and 3DS and not necessarily the Switch. Even the big AAA western publishers like EA and Activision benefit from choosing the platforms with the biggest audience. That's why cross-gen releases take years to taper out. That's why Ubisoft just announced a Wii game this year. True generation exclusive games that aren't 1st party are a rarity.
TL;DR - Nintendo's "support" for the 3DS is to continue manufacturing it, publish some games from partner studios, and allow 3rd parties to continue making games for it. The PS2 sold another 40 million consoles after 2006 using exactly this strategy of post-gen support. Of course the 3DS isn't going to sell like that now, but it's a solid course and a key part of Nintendo's plan for the next few fiscal years. It's good for early next-gen adopters, it's good for late last-gen adopters, it's good for gamers on a more modest budget, and it's good for kids.