I think most cryptocurrencies will begin to shed their blockchains. They're beginning to get unweildly, especially for Bitcoin (17GB). There's no need to retain a list of all transactions. You only need a consistent set of balances.

Also the energy cost of mining is beginning to become a legitimate environmental concern. I think the new slew of proof of stake currencies are going to give the proof of work currencies a run for their money (pardon the pun).