Can the PS4 keep its 50% Market Share even if the NX is included? 

For the PS4 to achieve that. It just needs to beat the total of XONE (Currently at: 21mil)  + Wii U (No more than 14mil) + The NX (???) 

If YES! What % will the PS4 get? 

If NO!  + When do you think the PS4 will go below 50%? (1st, 2nd, 3rd+ year of NX?) 

Will NX out sell the Neo? The answer to your question is yes 

Well Wii U marketshare will continue to diminish at a more rapid rate as Wii U sales slow down/PS4 sales continue. PS4 continues to gain marketshare over the Xbox 1 also as it outsells it weekly worldwide by a considerable margin. So by the time the NX comes out, the PS4 will probably have over 60% marketshare. I could very well see the PS4 maintain at least a 50% market share over Xbox 1 and NX considering the huge userbase advantage the PS4 will have over the NX when it comes out and the huge headstart/gap between PS4 and NX. It will be a challenge for the NX, not for the PS4 really. Or we might see the Xbox 1 losing the most marketshare whilst the NX gains. We shall see.

I think by the end of NX's second year PS4 should be below 50%

of course it all depends on how powerful NX and PSNeo are

NX is going to surprise us all.

That´s all I´m going to say :)

Depends on Nintendo's long term strategy which they have yet to divulge ...

Can it? Yes. Will it? Only if the NX is a truly massive failure.

Let's say the Xbox One ends up this generation somewhere around 40-50m. The Wii U will be around 14m. That's already 54-64m; making the PS4 need to reach 108-128m to keep its 50% marketshare.

Now, let's say the NX turns out to be a bigger flop than the GameCube and sells only 20m. That would represent a toal of 74-84m; making the PS4 need to reach 148-168m.

You see, even if the NX flops, it will be very hard... unless you think the PS4 will surely outsell the PS2.

That applies only if you include the Wii U into it. Including the Wii U into the marketshare(once the NX is officially released) makes as much sense as including the PS3 into the marketshare in my opinion

Umm, your numbers don't make much sense ... 

74-84m/148-168m =/= 50/50 

The PS4 would only just have to sell the as much or more than the X1, WII U, and NX combined so why would it have to double them combined ? 

You're right, this doesn't make any sense. I don't know, my bad..... always sucked at math.

I'm off to bed after this one, bye.