I am continually baffled at the 3DS fans that seem determined to spite Switch owners and seem to want it to fail in favor of their ailing system. The 3DS was bad hardware when it was released! Why wouldn't you want your games to be played on better hardware? Because honestly, it's library is what made the 3DS great in spite of itself.
Now, maybe you don't have a Switch. So then the games you want trapped on the 3DS will be waiting for you when you do get one. And if you're never going to buy a Switch, then really, why should Nintendo support you?
Really, the only thing the 3DS offers over the Switch, besides its library, is the 3D (barely relevant at best, and nonexistent for 2DS owners) and its dual screens. Now if Nintendo wants to create some interesting dual-screen usage games, then yes, the 3DS makes sense. Something like a Hotel Dusk or the original 999 (even though that has been ported to single screen systems) would absolutely sing on the 3DS and validate its existence.
Small ports done by smaller teams or outsourced teams could also be great. DKC or 3D World were mentioned. If it seems profitable, then sure, why not extract more money from the large base of 3DS owners?
But Nintendo really needs to focus on its future, which is the Switch. I'm not sure why they aren't doing cross-platform ports for upcoming games like SunMoon Ultra and Samus Returns. Maybe they don't have a good pipeline for doing so, which was definitely a mistake.