By the end of the year, switch will beat ps4 by a million or 2 which is nothing special considering the popularity and portability factors of switch and the age of ps4.
That would be true if everything stays at the current speed.
But while Switch should accelerate during Summer and boost in Fall with all the announced game releases during that period, and then go into overdrive during the holiday season with Pokemon and probably Animal Crossing this year, PS4 will mostly slowly slide down in sales, even with a 50$ pricecut, and just boost a lot for Black Friday.
In the end, the difference should be more around 5M, if not even more than that.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
List as Google Doc: https://docs.google.com/spreadsheets/d/1aW2hXQT1TheElVS7z-F3pP-7nbqdrDqWNTxl6JoJWBY/edit?usp=sharing
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/