This sucks for me, as a 670 owner that recently bought an Asus ROG Swift monitor (GSync 1440p)
I was planning to pick up a 970 with the intention of getting another and end of life when its cheap for SLI. Guess that plans out the window, and AMD is not an option. What to do, what do to...
If AMD is not an option, then you've got very few options. 970 is still a good card. My initial plan was to get one now(which I did), and maybe SLI it later on, but that was largely because of Nvidia's claims about having dual GPU VR rendering, which they've conveniently not said a damn thing about since! lol
My plan now is simply to enjoy my 970, which I'm still getting fantastic performance out of and for a great price, until maybe later this year or early next year and trade up. I'll take somewhat of a loss on the 970, but not a huge one(not like owners of 780Ti's and Titan's are facing if they want to trade up) while having a great card all of this year for games like Witcher 3 and GTA V.
So yea, it looks like you either buy a 980, or wait. Or pick up a 970. I went from a 670 to a 970 and I'm quite happy with it still. If you've got a 1440p/144hz display, I imagine its killing you not being able to utilize it fully.
I suppose one other alternative would be to take this year to clear your backlog and play lots of older games. A 670 can still do 1440p/45-60fps with a fair amount of last-gen games and older.