I would hate it to be the last of the 3DS games to be honest I would love to see more 3D pokemon games since i still think that they can make something more with what they got at the moment.
Switch will enable them to make the 3D models/environments far better, unless you mean the 3D
effect, in which case they've done away with it completely in Sun and Moon aside from a mini-game, and even then it tanks the FPS from what I hear.
Game Freak is struggling to fit main series Pokemon on 3DS. This is a fact. Anybody hoping it stays on 3DS longer don't actually give a damn about the franchise, and only want to not have to personally upgrade devices, even though it's inevitable that they'd have to eventually as the 3DS won't be around forever.
And to anybody skeptical of the Switch's performance and/or role: Nintendo would not have made a handheld/console hybrid if they weren't planning on moving their handheld games over to it. They would not have consolidated their development teams if they didn't want to move to a single platform. And
if it does poorly, do you honestly think the 3DS will last much longer? What games are people even actually expecting it to get next year? Nintendo themselves even said 2018 would be as far as they're willing to support the system, and that is going to just be with some small, late projects if past systems are anything to go off of. If Switch doesn't replace the 3DS, something else will.
The 3DS has only been doing as well as Pokemon GO/Gen 7 allowed it to this year. When the only thing truly keeping your system alive is a single game, what's the point in keeping it there when you could use that influence on your next big system, especially when that next big system is a
handheld? I can see them doing a dual-platform relealse for the 2017 games, but I'd expect full Switch-exclusivity afterward. Giving people a reason to stay on 3DS cannibalizes their own product, just like the 3DS horribly cannibalized the Wii U. They can't keep supporting two platforms like that.