I can't think of any instance where a console manufacturer has lowered their original forecast in an attempt to do much better than expected. What their downward revision to 13.5m (after the original 16m had already been revised down to 15m before) most likely means is that it's going to be all downhill for the PS4 after Black Friday. Last year's December in the USA was already weak, but in 2019 it's going to be even worse. Europe has less emphasis on Black Friday, but holiday sales overall will also be down from last year. In Japan it looks like Sony won't match last year's deal and perhaps won't offer a deal at all.
Afterwards, January to March 2020 will be uneventful for PS4 hardware sales except for Final Fantasy VII at the backend. The PS4 should be down significantly year over year for the final quarter of the fiscal year, hence Sony's forecast.
FF7R is big though... thats like Halo levels of big.
Ghosts of Tsushima is probably like gears levels.
The Last of Us Part 2, is alot bigger than a halo title is.
Theres stuff for 2020... that should make new consumers want to jump on board, ontop of the already really solid lineup & library of games there.
Also like I said, that forecast down to 13.5m, is something thats gonna be blown past imo.
The system selling power of games diminishes the further into the cycle we go, especially when it comes to franchises that already have a presence on the system.
FF7R & TLOU2 will both be huge sellers and will definitely move some hardware but the wont stop the decline.
As for the forcast getting blown past, that's not happening, they already adjusted it down twice this year and if they wanted to lowball than they would have done so from the beginning.