So lets say the NX comes out 2016. The Xbox something and the PS5 come out 2019. Will the next nintendo console launch late like 2021 or will it be cut short to compete in 2019? 

Its a good thing, Nintendo launching early is bad.

The NX will end traditional Nintendo console launches, so no. Systems after the NX will just be iterative hardware upgrades, part of the same platform with all the same games, just like the iPhone. So the NX console 2 will just be a more powerful NX console 1 with maybe a minor new hardware quirk and an update to the OS which will still be downloadable on older models. In fact, I wouldn't be suprised if we did see the NX2 in 2019.

Also, I don't think there will be a traditional PS5 of XBO successor, since I think they will instead go the way of streaming with PS Now and some sort of PC console hybrid service with Xbox, so no's all around. Also, we won't see a successor to either until 2021, so no's full circle.

no because nx will have a 4 year lifespan

You really think there's a chance that not only will the NX launch after only four years (sort of almost plausible) but then its successor will launch only three years after that? I don't think that's realistic in the slightest. That's a complete console overload, and that's coming after the Wii U's failure to stick. On top of it all consider how it can take years before Nintendo's able to develop enough games for their systems to make them more appealing.

Apple gets away with it with both phones and the vastly more expensive PCs. Why? Because the content transfers and the old products don't become obsolete imediately after. Nintendo can do the same thing with the NX line, and it would work.

Honestly, we don't even know what the NX is yet. We merely know what it isn't. It isn't a disc based console. I think if we actually had proper specs on what we are talking about, it would be easier to predict.   For example know the power of the console and its cost really have a major impact on alot of these topics.   We technically don't know what we are even talking about here. 

We know that it's part of a unified platform of systems, we know that it's meant to absorb the Wii U's architecture, we know that it's sharing a library of games between a portable and a handheld, we know that it's tied to the new membership program which is tied to DeNA which is tied to Nintendo's new mobile initiative which is tied to Nintendo's plans to spread brand awareness for Nintendo and it's IP which is tied to Nintendo's recent plans utilize its IP in other media like TV, film, and theme parks, we know that it's powerful enough for Square to consider porting DQ11 to it, we know that the console is keeping the gamepad, and yes, we know that it isn't a disc based console.

I know that isn't much, but I think we can squeeze in a few minor educated guesses from the extremely little we do know so far.

Then it would have a wii u life cycle. I don't see that happening because it will probably sell a lot better than wii u. The only way it would happen if the next Xbox and Playstation are ALOT more powerful.

read the question again