Well if history is any indicator, not by much. They are in fact dropping right now. For example my EVGA SSC Gaming ACX 2.0+ cards were $360(US) when introduced in Spring 2015. They are now down $20-$30 depending on vendor.
But I don't see the 970s dropping to the mid-$200s killer deal for example. The 680s didn't drop much in price when the faster Kepler refresh 770 came out. Same with the 770s when the 970s came out. Retailers just let their stock run down of previous cards, and in some cases actually jacked the prices up, which really put people wanting to go SLI for the previous generation in a conundrum (I was one of them wanting to get a second 680 for SLI when the 770s were released).