Any btc price prediction should be taken with a grain of salt.
Is it possible? Yes
Probable? Maybe, if this decline is structurally similar to $250 to $70 decline in the summer of 2013.
Bitmain and Innosilicon (competitor) are producing vast amounts of mining machines and people are buying (so far).
Right now when mining at a cost of 10c/kwh, breakeven point is somewhere at $7000-8000/btc.
How likely would be a five-fold difficulty increase in 1.5-2 years?
Quite likely as it would take slightly less than 4% increase in difficulty per adjustment period (about 13 days).
last five adjustment periods were 6.91% on average.
last 10 adjustment periods were 5.7% on average.
With 5.7% adjustment per 13 day period in the next 1.5 years, btc price would have to be $70000-80000/btc for miners to break even when mining at the end of that period (end of 2019, early 2020).
These are excellent points. I also did a similiar calculation a while ago and realized that btc was not profitable to mine while around 6k. I noticed very few people make an effort and do this kind of analysis. Like you said earlier, people are lost in their emotions instead of keeping a rational outlook or dig a little deeper to understand the costs of mining. Based on that the 60k projection appears suddenly not so outlandish any more.
Alessio Rastani is a financial expert who compared recently the mining of bitcoin with the mining of gold. If Gold prices rise too high, then too many companies invrease their efforts in minining and after some time the over supply will lead to decreasing prices until a good portion miners reduce their efforts or go out of business. I recommend to look at it.