Nintendo confirmed already that the Nintendo Switch would NOT be replace the 3DS, so I don't think Sun and Moon will be the last on the 3DS somehow.
Let's hope not. Not everyone can immediately buy a Switch, it would be stupid to change this soon. How many games have really released for 3ds? That said, Sun and Moon were disappointing with no 3D effects whatsoever... I did hear rumors about a Pokemon Stars for Nintendo Switch. But I sincerely hope they won't leave 3ds this quickly with Pokemon. I can get a Switch before Stars is said to release, but that isn't the same for everyone. (Plus I am not even sure I want the Switch. I prefer handhelds and hearing the handheld style might only have battery power for 3 hours before it has to be put back in the console to charge is putting me off.) So naturally I would prefer they stick to 3ds for a while to come! (And still holding a torch for a 3d version of Gold and Silver )
Really? I have no problems whatsoever when it comes to online play. You sure it isn't your internet? Because I have glassfiber with a constant speed flow and I never had lag. Which makes sense because the system was made to handle 3D games and Sun and Moon has zero 3D features... If that Switch to last as long as my 3DS does and is chargeable just like the handheld, I might buy it sooner. If not I will buy a iPad first. (I need a new one, but atm it is between that iPad and a Switch.)
Now that Monster Hunter XX has been announced for the Switch, and has a fair bit of cross-compatibility with the 3DS version...
I think that the most likely outome is that the next Pokemon games will be available on both platforms.