Dollars in to dollars out I think the ROI will settle in at 10 +/-2 months so long as there are no new quantum leaps in technology, again.
The thing with ROI is that some miners are not incorporating the big jump in difficulty in their calculations. Or incorporating a smaller number compared to what the stability will bring. Hell, maybe some new miners are forgetting the reward being halved around the time the first ASICs (are supposed to) hit the market.
That will make ASICs look like a good investment with a reasonable value of say, 10 +/-2 months for the time needed to recoup initial investment. A lot of pre-orders are in and when the "real" difficulty hits that ROI could jump to 12, 16, 24 months ...
Every time I get excited about my returns I remember that I forgot to divide that revenue in half... Then I kind of feel like Meh... Maybe I'll invest in ways to overclock my Jally