My impression since the beginning was that they would cut the price around March 2015, 50$ at first, it will give a nice early in the year boost (around the release of Bloodborne + The Order and some other valentine's day crushers from third parties)..
Then 50$ every year to 18 months depending on sales data .. so sometime in 2016 we should have a PS4 at "normal" game console price, 300$... 200$ by the end of 2018 would make sense.
Obviously they could cut by 100$ chunks.. that would be much more impressive! (and it would stun MS and Nintendo to have to deal with a 300$ PS4)
EDIT: they probably have a bottom monthly sales number they want to reach before lowering the price, or any signs of decline from what they consider their realistic "baseline"... as soon as people loose interest, they'll lower the price to get people who were a little less interested in their console, so on and so forth, like MS did this year, they found the real 'market' value of the XB1, which is 300 - 350$ (depending on the value of the bundle)... obviously sane people think the PS4 is worth more than the XB1.
