I actually like that they are still supporting the 3DS. I'm not a 3DS owner, but if I was I would appreciate it.

They pretty much have to.

"Doug Bowser, head of marketing over at NoA"... yeah, he would be. For their sake, I sure hope the switch is their direct successor.

Gen 8 has already been confirmed for Switch. It is the direct successor

Do you mean to say Gen9?

What would be Gen 8 if Pokemon Switch is Gen 9?
Ultra Sun and Ultra Moon? Those are just follow ups in the same sense that Yellow, Crystal, Emerald, Platinum, and Black/White 2 were for their generations.

Ah, Pokemon I was thinking it was confirmed as the Gen 9 successor to 3DS. I have no idea as to Pokemon.

Oh, I see.
Well to give you the idea.

Gen 1: Red/Blue
Gen 2: Gold/Silver
Gen 3: Ruby/Sapphire
Gen 4: Diamond/Pearl
Gen 5: Black/White
Gen 6: X/Y
Gen 7: Sun/Moon
Gen 8: ?/?

I'm getting old. As far as games go, B/W is a game I still consider new.

The main difference is that the PS4 is the direct successor of the PS3.

The PS3 would not slow the PS4 down in the long run because game developers wouldn't be able to create next gen games on a weaker console and in case you forgot, Sony actually did stop supporting the PS3 by not releasing any big first or second party games on the system anymore... The Last Guardian was supposed to be a PS3 title Sony fooled those who bought a PS3 and now made them buy a PS4. 

Of course shutting down all services PS PLUS, PS Now, stopping production early would be stupid because there are lots of people who haven't bought a PS3 and since its cheaper than the new PS4 it's easy sales, Nintendo doesn't have to shut down the 3DS like they did with the Wii but meanwhile...

The 3DS is getting yet another line of Pokémon games, a Metroid game, Kirby, Monster Hunter, Layton all of which could have worked on the Switch even if they'really just spin-offs they would've boosted sales. Why do you think nobody liked the Pokemon Direct reveal? because they wanted Pokémon Stars on Switch. Why do you think all these "why not for Switch?" comments keep popping up because right now we are getting mostly ports. WiiU owners hated Directs because Nintendo would announce all the big games for 3DS and just indie games or nothing at all for WiiU.

The problem is not Nintendo keeps selling more 3DS systems, the problem is that they're continously hinting that they could see both Switch and 3DS co-existing together in the future which either implies they will keep supporting the 3DS by releasing more games for it OR make a successor which Switch is supposed to be.

This will only slow game production down for both systems and one system will be favored over the other by both consumers and third party developers just like in the WiiU - 3DS days. Again Nintendo doesn't need to shut down all services and end production on 3DS they need to stop releasing these big games for it and instead focus on bringing big games, both first and third party, to Switch.