The switch actually allows for an easier vertical configuration than the gamepad did, since you can take the joy-con off.
If they really wanted they could make one of those flexible holders you find on phone stands and add joy-con rails to it.

The holder would grab onto the Switch and you could add the Joy-con left and right in a Vertical configration. Sure, it might look a little wonkey and you probably wouldn't be able to charge teh Switch while playing, but it's possible.

Switched is designed to have alternate control schemes. Not impossible that a specific Joycon/control option could be designed to be used with a DS/3DS mode. I wouldn't expect a docked mode... why?

Oh believe me, I have my 3DS and my grandpas DS with me 

Personally, I'm waiting for the dual-screen Switch model.

Move on.

Nintendo will not design a Switch model just to play DS/3DS games. As I pointed out earlier, Switch screen is roughly the same size as both screens so it would end up pretty pointless anyway.

Hell no, have you seen the pictures above? They're stuff of nightmares, anyone that drops his DS/3DS to play the games like that is clearly out of his mind, thank the gods I've never felt the need to try that in my Wii U.

kid icarus uprising will be very hard

You know games can played on Switch while vertical right? There a few Neo Geo games already doing it.   

The black square at the bottom is where the bottom DS/3DS screen would fit 

Umm, even if there are some ways to make in undocked, those same ds and 3DS games would look hella ugly magnified on TV.