This, imho, is the single, possible saving grace for the Switch. If Nintendo drop 3DS support and put all their efforts into developing games for a single hybrid platform, there might be enough first party titles to make it worthwhile. They will have to step it up in terms of breadth of games from the **** poor show they gave us with the Wii and WiiU, though!
Here's a hint for you, what does discontinuing support for the new 3DS which in many areas only launched what, Sept-Nov 2015 say about Nintendo's commitment to supporting handheld long term?
If they discontinue support for the 3DS then Nintendo are actively screwing millions upon millions of buyers, which only scares people off buying a Switch for fear it will do badly and they'll want to dump support for it in 18 months.
Likewise what would dumping support for the 3DS do to third party developers, who will question if Nintendo have any long term commitment to their devices. Will they want to invest in a game now that may come out after Nintendo give up on the Switch?
Also most importantly, if they gave up on the 3DS and they were going to switch so many devs over to a single platform.... why are there so incredibly few games ready for launch?
basically the decision on if to continue 3DS support after the Switch launch would have had to happen before the new 3DS launched, because it's too close. They could have cancelled production on the 3DS and focused everything on the Switch, they didn't.
There are also currently way way way more 3DS in use, so in terms of software sales, the 3DS is more profitable. They wouldn't dump 3DS support for the reasons above till at least 18 months from now I'd think, and frankly if and only if Switch sales continue going well outside of launch. Wii U had 3mil on launch quarter then 3mil per year for 3 years, then down to 1mil last year. Until it proves itself by say selling at least 10mil in the first year, they won't even consider dumping a significantly wider user base till Switch can provide similar numbers.
Again they may do it earlier, but what does it tell you, if it's not selling enough or if they aren't making enough profit off you they'll dump support? Look at the lack of games at launch, the lack of games coming over the year, if the 3DS gets dumped after 18 months, what chance does the Switch have frankly.