I disagree with this view. I don't think there is a bottom line for cryptocurrencies. Many people say that mining prices are the bottom line, but I don't believe it, because when bitcoin falls quickly, miners will choose to stop mining instead of buying bitcoins!
Yeah you are right just as nobody knows the top price of bitcoin; nobody knows the bottom price of bitcoin too. Price depends upon the investment capital; if the demand for bitcoin increases and people put their money in bitcoin the price will go up and if people do not invest in bitcoin the price will automatically drop because of no or very less demand.
Those speculation is baseless, if you look at how bitcoins proliferate the are lots country recognizes and eventually using bitcoin as a medium of payment, and remittances, and besides these systems integrity is still there. there's no reason that the price will go to the the bottom, actually it is based on supply and demand and the world economy it self.