You can never tell what is going to happen to the trade price of cryptocurrencies, but most people probably don't expect the situation to suddenly and quickly reverse itself. What's more, many ethereum mining enthusiasts expect AMD's current cards to stop performing as well as they do now within a few months—tests have shown a severe reduction in performance as the complexity of ethereum calculations increase. Nobody knows what the problem is for sure, or if a driver update might fix it, but an RX 480 or 580 bought in the last month might never pay for itself once you factor in electricity costs.