The pro will keep dropping in price and push the standard ps4 price down. At some point I believe the pro will become the standard ps4 model especially when the ps5 arrives and the ps4 pro takes up the budget model position for a few years. Hopefully PS VR will gain traction as well adding to ps4 demand. 

Dare I say even a Sony Switch competitor based on semi-compatibility with ps4 may even be called a ps4 like ps4 go or something like that.

Lots of variables in what could happen in the playstation ecosystem most of which is positive. The Switch as a low performance platform is not really a competitor for the same gaming space and only caters for certain genres of games but the Xbox one models are competing directly but I feel even though the X is brilliant hardware the momentum for the xbox brand is slipping. PS4 is in a great position for the next 2 years.

Because a 500 GB XB1 S with Halo 5 and Master Chief Collection retails for $229, with another free bonus game, and a month of XB live included. 

Once you subtract all the freebies the XB1 S is already under $200. Now imagine we are halfway into 2018. Sony is pretty much forced to price base PS4 at $200. 

For 85m sales PS4 would have to drop by 50% next year.

achievable if PS4 gets $199 price cut and also FF VII episide 1 get released in Japan or any other major title get released in Japan during the holiday season (nov, dec).

I agree. 100m+ by mid 2019. The PS4 will eventually sell more than the PS1 but less than the PS2.

It's gonna sit somewhere right in between.

Are there still that many people who don't have a PS4 that want one? I certainly wouldn't rule it out, but I'd think it far more likely if the Pro had been a bigger upgrade than it was.

With the Xbox actually having a decent piece of hardware people are fond of, it just seems like this will be the first full year that the PS4 doesn't have outright domination of the console market like they did with the Xbox1 and Wii U. Again, with how big the price drops often are I wouldn't be surprised (I'm seriously considering picking up the Pro for God of War IV and a couple other titles myself), but this will probably be the most challenging year for the PS4 yet. Fortunately for Sony, their 2018 game lineup looks extremely impressive.

I go for 94 millon at the end of 2018.

It will sell more or less the same as in 2017, unless somehow XB1X sales will explode in 2018, stealing a good chunk of the market. In that case 95M is possible.

I think it is up to Sony whether this happens or not. $199.99 PS4 + $299.99 PSVR Bundle should make this very easy. Looking for $179.99 PS4 Slim during the holiday, and $199.99 PSVR Bundle.

PS4 should be able to best 2018, I'll bet 95 Million Shipped.

I still think 2019 can do even better if they have a PS4 Slim, PS4 Pro Slim, PS4 Premium, PS4 Portable of some kind, and PSVR Pro, but we will just have to wait and see.