I think everyone has made the point but I want to add some things that haven't been mentioned yet (or they have and I can't read)

• Nintendo's markets were split - One interesting thing about the DS and 3DS was that the US was the biggest market (in terms of total sales) for the DS but Japan was the biggest market with the 3DS. At the same time, despite the Wii being a huge hit in the US, in Japan, it sold less than the NES and SNES. Basically, any console Nintendo made was going to appeal to the West and any handheld was going to appeal to Japan. And each system needed 3D Mario, 2D Mario, Mario Kart and now Smash Bros. Nintendo makes about 7-8 games a year. In a 5-6 console life, Nintendo was making a lot of repeats. Also, as Rol alluded to, it's not effective anymore to focus on two systems. Development times are getting longer and longer.  You can't develop for two systems anymore
• Droughts - This goes along with the first point, but Nintendo saw that a major reason the Wii U failed was because of hardware droughts. The Wii U's first two quarters were actually pretty good. The system was selling well in the beginning (and it had a ton of third party games). The system fell off in 2013 as nothing released for it (there were other issues too but this is the one Nintendo is honing in on). Nintendo is able to have a constant flow of software because they were only making games for one
• The "third pillar." - I think you misunderstood why Nintendo had the third pillar and it has nothing to do with backwards compatibility. With the "third pillar" Nintendo was giving themselves an out. If the DS succeeded, the Gameboy brand would fade out. If not, Nintendo would say "lol, just kidding. Here's a new Gameboy." The same is true here. Nintendo wasn't sure if this new strategy would work so they are keeping the 3DS alive. If the Switch failed "lol here is a new 3DS." The New 2DS XL is not unlike the Gameboy Micro. Also, unlike the Wii U, it's still selling. Kimishima has said they aren't sticking to the structured console lifecycle, so Nintendo will "support" the 3DS until it stops selling. The "third pillar" was just a Plan B as the 3DS is now.
• 3DS Games - One thing you mention is that Nintendo is still making 3DS games; however, all of the games they are releasing are made by other developers. Pikmin is from the new Artoon (not sure their name). Ever Oasis is from Grezzo. Pokemon Company does their own thing (they are actually a separate company), and Metroid: Samus Returns is being made by MercurySteam. The only game Nintendo's internal companies have made for the 3DS is Fire Emblem Echoes.  
• Shareholder's Argument - You made this weird argument about shareholders which tells me you don't do much with stocks. Investors care about returns. If Nintendo can do that with one system vs two, then what do they care.  The  Board and Management have a fiduciary duty to the shareholders to maximize the value and longevity of the company. If the two system approach is not going to do that, then they are expected to change course. The shareholders might be more upset if Nintendo tried to have two systems and shareholder knew the strategy wasn't feasible. They won't get shocked because of a "lowering of the ceiling." It's a dumb point because earnings will likely be up, and Nintendo's share price is increasing
• The Nintendo Switch is a handheld - The reason your arguments sucked is because the Nintendo Switch is a handheld. You argument relies on this idea that Switch is not a handheld despite being able to play it anywhere (which is the whole point of a handheld isn't it). 

Actually only thing that I wrote and that is my opinion and very strong point, is that "there is no reason at all to release another handheld platform or to continue with DS line alongside Switch", and that is based on clear facts I mentioned (Nintendo merged their home console hardware and handheld hardware divisions, and they merged their home console software and handheld software divisions, fact that Nintendo talked and admitted they can't any more support effectively two different platforms, fact that Switch is already handheld in same time). There is always posibilite for different handheld platform or to continue with DS line, but point is that is highly unlikely now when we have Switch (there is even possibility that Nintendo will abonded Switch next year, but that also highly unlikely), and instead we will almost certain have Switch Mini/Pocket, and thats what most people here are saying to you, while you from some reason keep pushing highly unlikely scenario.

Ehhh.. I dunno man. I feel with the Switch on it's own makes the most sense to me. All the development studios working on the same system to get a steady flow of games out along with periodic smartphone game releases seems to be what they are going for.

Again, because apparently this still hasn't sunk into you, you are treating your interpretation of what these facts (and opinions) mean as if it's an objective fact, as if your interpretation is 99.9% correct, and it's not even remotely possible you might be wrong.

This is not true.

The fact that you say ""there is no reason at all to release another handheld platform or to continue with DS line alongside Switch" means that you are ignoring facts and information because that is objectively false. The fact that you seem to equate Nintendo releasing a 3DS successor with the likelihood of Nintendo abandoning the Switch altogether next year is as clear of an indicator you can get of just how arrogant and over-confident you're being.
 That's really all there is to it.

Yes, there is no reason at all to release another handheld platform or to continue with DS line alongside Switch, and yes I am very confident about point that Nintendo will not release another handheld platform or to continue with DS line alongside Switch.

Erm there main system is a handheld, what did people not get about their Fusion conference, going forward they will have one system to do both, this was outlined like 2 years ago before switch was even announced.

Sure there is! You just dismiss them, while shitting on others for apparently "ignoring facts" when in reality all they're doing is taking those facts into consideration with others you're dismissing, and coming to the conclusion that it's not nearly so obvious as you want to pretend it is.

so when is the whole, "Nintendo might make a seperate 3DS successor" talk going to end?

like if 2 years from now Nintendo still hasnt announced one will you still think of it as a possibility?

They'll likely make a more handheld-oriented version of the switch later But yes, 3DS is going to die.

Switch is the nintendo handheld. After they increase battery life and slim down switch, there will be no point for a new DS.