No no no. The Swtich is not a Gameboy. It's a home console. Nintendo has said this repeatedly. The 3DS is not even a gameboy. if you believe it is, then I have a cartridge of "Kirby's Dreamland" for the Nintendo Gameboy, how can I make that cartridge work on a 3DS. An example of an "upgraded console" would be the DSi vs the DS, or the PS4 Pro vs the PS4. They play all the same games with a spec improvement. When you talk about upgrades, you're talking about entirely new platforms. Those are two completely different things.

This possible replacement for the 3DS - I can't begin to comment on it. I have no idea how it would work, but please note it could have the exact same games and just run completely different cartridges, and it doesn't matter if it can connect to the TV or not any more than it mattered for the PSP. Don't think for one second that Nintendo isn't fully aware of how many Wii U owners also owned 3DSs and how many copies of basically the same game they sold to these owners in mutliple form factors. Don't think for one second they're willing to throw that away so easily.

Then they kill the switch.... and/or the switch makes this new DS not be able to be successfull, one or the other.

Who said it had to be less powerful? It just would need to be cheaper and most importantly, accept different cartridges.

You forget the Wii, which is as we all know two Gamecube duct-taped together. So, the new handheld is obviously two 3DS duct-taped together. So, the new handheld has four screens, therefore the new Nintendo FS. As a new feature it can play two 3DS-games at once, so it is a system for all people with growing backlog that have not enough time to play all their games!

So you want a 3DS successor thats more powerfull than a switch.... but cheaper?

If that was already possible, why didnt nintendo just do that from the start?

Bingo. If it's a close third in the console war I consider it a success, so long as their revenue helps. XBO is a distant second and successful anyways. The predecessor was de facto first place or second place and was losing money up until half the gen and the original Xbox was the second best selling console and the Gamecube succeeded whilst MS considered the OG Xbox a bomb. They literally burnt profits to feed the fans... 

In fact, I think the only time where someone lost money AND was third place was the PS3... 

But wouldn't it mean that the Switch would be a success, according to the OP?

They activate the Kill Switch and are done with it...

Why would you do that? Accept different cartridges for the sake of locking out people from software? Lets get this straight first off -- Splatoon not being available to 3DS owners to play (65 million of them) is not a good thing. It doesn't make Nintendo more money. 

Imagine if 3/4 of McDonalds could not serve french fries, that's not a good thing for McDonalds. 

More likely what Nintendo would actually do is introduce a higher end Switch in 3 years time or so, something that has a higher-end Tegra X3 and can occupy the $300 price point. The current Switch will be die-shrunk down to 16nm or 10nm, as be incorporated into various lower price models (ie: $229 basic, $179.99 Switch Mini, $149.99 Switch Home, etc). 2DS/3DS is phased out entirely by those models. Software is cross compatible between all Switch devices. 

That's far more likely. You want your software library to have access to the widest consumer base. 

Who said it had to be more powerful?

I have not made any comments about power. There are plenty of ways you can reduce the cost of something like the Switch that have nothing to do with power.