Goldman Sachs are foreseeing most cryptocurrencies will go to zero. Other such as Peter Schiff also see bitcoin will be worthless. Their contention is that cryptocurrencies has no tangible value. Strongin of Goldman Sachs believes that due to long transactions times the currency has no long term staying power. He also feels that the cryptos are in a speculation bubble.
Although I am not a fan of Peter Schiff or Goldman Sachs, I also think the cryptos are in a bubble and their valuations have no support. I do believe that the block chain will be incorporated into some cryptos that will survive due to their utility. But many of the cryptos will not last, considering there are about 4,500+ different coins (Source: cryptocoincharts.info) When I evaluate a coin, I am looking at what the coin is meant to solve or what is its utility. Also the value is contingent on how many are mined or in circulation. If the is no limit to the amount of coins in circulation, it will become just the fiat currencies. Overall the ability of the coin to be used with little transaction fees and little latency for the transaction to complete will likely determine its viability.