I think it would be too hard to calculate. With KNC releasing 200-400 MH/s hardware, Bitmain scrypt miners trickling out at (or before) the time of Zeus, and GAW's cloud service leasing out 100-500 MH/s units, there will likely be an unprecedented hike in difficulty between now and January of 2015 . Considering that LTC is currently priced is at 0.0105 BTC, it seems irrational to even consider the idea of this as an investment.