I dunno. If Sony were to launch a bare bones PS4 superslim for $200 ($150 for holidays), we might see another genuine surge in sales.

Sony limited PS4 sales last year. The thing was sold out during the holiday season. Had they produced more units, and kept the $199.99 price point, the sky's the limit on how much they could have sold. I am not sure what is in the works for this year, but only producing 16 million units, looks like it will land them in the same boat again. With Red Dead, Spider-Man, Detroit, God of War, and more yet to come, the only thing holding back PS4 sales is Sony themselves.

If they in fact think they can only move 16 million PS4's this year, then they are selling themselves short, and are taking a massive miss step with the platform. They have a numerous paths they can take to sell more units, continuing to drive up the user base, and stay more activily engaged with their consumers. Hopefully someone at Sony has some vision. It would be a shame to see them piss away everything they have built with PlayStation for a second time.

16m won't actually be the shipment. 16 or 18m my guess and there's no reason they can't ship the same the year after.

Yep. Even if the PS5 launches in 2019, the PS4 is going to be approaching 110M by the end of that year. And it's not going to stop selling even after the PS5 launches. Especially considering it has yet to hit a permanent price point of $199. And going by sell through, the PS4 may have peaked, but it did it last year, not FY16, as shipments would suggest. 

If Sony planned for a pricecut or a new model, these would be included in their forecast. They only will change their plans if sales drop faster than they expected, but that wouldn't be a good thing.

Ps3 sold 15 mi between ps4 year launch and now, so, probably ps4 will have 100m at e3 19 and if ps5 is released at the end of 2020, it will make at least 130m at the lifetime.

Stagnation is a bitch at some point it is simply hard to keep on selling in a market that already has many PS4's and when you have second hand PS4's for 100-200$ on the market you also will lose some sales. Then again hardware does not make a big portion of the money it is the software/Ps plus etc.

They need to drop the price of the console.

Yes, it would be in their forecast for this year if they launched it this year. That's not what I suggested, I simply suggested a surge in sales following a new SKU. It could happen next year in the PS4's twilight years.