Thx Tigggger. Very helpful.
I guess there's no way to include the halving in your calculation. So we need to be aware the BE time (aka ROI) is likely longer for each of the electrical rates in your chart. As a very rough estimate, my guess is we can add 25% to the length of time to ROI.
You could do one on individual electric prices, and make a spreadsheet over time, mine is more of a quick and easy guide I'm afraid.
Diff rises have been fairly gentle for a while, but with this new equipment hitting the market for buyers, the innevitable Bitmain S7 self mine, the Hashnest S7 mine, the Pacmic V4 S7 Mine (and possibly LKTec/Innosilicon machines soon) I think the diff is going to get some sizeable jumps in the near future. My best guess would be to add even more say 50% onto the ROI dates, that should cover diff rises and the halving.
It's honestly hard to say. LKetc/Innosilicon are doing A3 and A4 chips at once ... I think they should have focused and did one then the other. I would not count them as a big factor right now.
Now Bitmain and how many S7's they do make will raise difficulty. Someday I still think a lot of A1 gear needs to come offline. I'm not sure how much this equals, but I think there are basic data centers full still in very cheap electricity places.