Given some of the recent ASIC releases and Volta on the horizon that 10 months could get a hell of a lot longer. On a positive note the release of Volta may see secondhand 1070/80's come onto the market and bring prices down to more sane levels.
Given the Titan V performance, I don't anticipate Volta making ROI significantly longer on Pascal cards - it's looking like a ballpark 20-30% improvement AT MOST, so noticeable but not game-changing.