good post about returns.
I also think the ROI especially on pascal will increase If you get the cards today, you will still have at least one new generation nvidia cards, which also will increase ROI from what we can see from the leaks and based on history.
New cards will be really expansive but i don`t sure that their cost will make them best ROI. It depends how you use your cards, can or can`t hodl and a big amount of other vatiables.
I saw the price of 1080Ti dropped about 3% in the last two weeks.