So, because it would receive a 100$ price drop, it would sell almost TWICE as much as last year for the period of jan-Aug? PS4 will never have a 20mn+ year, and absolutely not THIS year :).

I wouldn't say never since we don't know when it's going to peak, but I doubt it will hit 20M this year.

A price cut in the 2nd half of this year is exactly correct timing, because without it PS4 will be down year on year, that's almost guaranteed. And Sony does not want the negativity that comes with being down year on year in only the 2nd full calendar year of PS4's life. 

To have a 20 million year in 2016 PS4 only needs to grow by 40% over 2 years for one of those year to be a 20 million year. Peaking in the 3rd year is pretty much as common as peaking in the 2nd year. So a 20 million year is very much on the cards, in fact it is more likely than not.

Awe, I wanted a chart.

Good work anyway.

how much did ps4 sell from january to september 30th in 2014?

i understand what you mean,but,sony is a company which aims for profit before looking the market share...usually a price cut comes when sales gets slower or competitors get more competitive...

anyway,if they cut the price increasing the install base,it makes me happy,because it shoud bring us more games encouraging developers

Not a chance there will be a $100 cut this year.

I am quite confident it will stay flat or actually drop next year, while X1 will stay flat or have a small growth.

There will either be a $50 cut this year and another one next year, or there will be a $100 cut this year. Either way there will be growth 2 years running which makes a 20 million year very likely. PS4's peak year will be the full year is sells at $299, that will either be 2016 or 2017. One of those years will probably be a 20 million year. When the first full year sells >14 million a 20 million year is inevitable unless something goes horribly wrong. If you think something will go horribly wrong you should say what you think it will be.