A lot of people I know talk about the cryptocurrency bubble bursting in the near future. In fact, many economic speculators talk about this as well.
I think though that the people talking like this either A: don't understand the technology well enough. Or B: are applying olde economic rules to a very different type of economy.
I think that the more likely scenario is the bursting of the traditional currency market. USD, Yuan, Euro. The cryptos will continue to rise and eventually enough people are going to cash out. This is going to cause a huge influx of those currencies electronically, because there is no real backing value and no real cap on how many can be in circulation, as compared to a set number of crypto. When this happens, those currencies will become hyper inflated. Now how this will affect cryptos in response....who knows?