Delay of transactions:
I found it difficult for any crypto to be widely adopted for commerce and day to day life, if transactions took anymore time than any normal bank transaction. Steemit, bitShare and EOS, can handle enough transactions per second to be possible for day to day purchases.
Volatility:
I also found extremely difficult for commerces, retail, services to be able to accept any crypto as payments since it was so volatile, not many would like to assume the risks of Volatility. Steemit and bitshare also try to solve this issue by creating an asset (Smart coin) that is always worth 1 USD in cryptos.
Fees of exchanges and spread:
Entering and leaving cryptos to any fiat had costs that would make it non viable for regular people to use it as payment methods.
High power consumption:
There is a trend of going green, preserving environment and using renewable sources of energy. Bitcoin, and other alt coins that use PoW protocol consume so much electricity, I can not imagine a world where some transactions cost most to make than the actual value of the transaction. That is extremely inefficient. I really love bitcoin but its power consumption is something to think about. DPoS and PoS protocol tries to solve this issue, however I'm still worried about centralization in those protocols and trusting issues. Anyone any thoughts about this?