There is a lot of hype around cryptocurrencies today and it could be easily be a bubble similar to dot-com one. Cryptocurrencies themselves are not backed by anything and a lot of companies get funded through ICO are completely "experimental".
But dot-com bubble left a great infrastructure after itself which allowed internet companies that we all know today to prosper. Similarly even if cryptocurrencies will turn out to be a bubble and will cost a little above zero someday there are already discoveries from computer science to economics and psychology that have already been made.
Even if bitcoin and others won't survive it is not an experiment emerged out of nothing. Bitcoin was proposed as a different way to have currency in which repetition of 2008 financial crisis is impossible. The problem is real and failure to solve it is actually a valuable result.
And of course there is a technology that powers cryptocurrencies that has a great potential:
image source: commons.widkimedia.org
For engineer this might be a great opportunity to become an expert in the technology in an "organic" way by following its evolution and become a highly paid professional on a potentially big market of blockchain applications development.
Overall besides being interesting hobby developing skills in cryptocurrencies and blockchain development seems to be relatively safe and promising investment.