This is the scariest thing about BitCoin, this efficiency bubble. What happens when the world's miners decide that a different crypto-coinage is more profitable?
I don't believe that the difficulty parameter in BitCoin adjusts very fast (every 2016 blocks or ~14 days) and you could have transaction speed disruptions. If a block doesn't solve in 10 minutes but instead an hour, you'll have a lot of very unhappy people waiting for transactions to seal and they'll abandon the network after selling off their assets. That's just the time aspect, you mention the transaction fee aspect, and that will drive people away as well if they start to creep near what legacy financial systems charge. The declining block reward in BitCoin guarantees that transaction fees will increase because of the limited capacity of the consensus network's data-storage/transaction block.
I don't believe that the difficulty parameter in BitCoin adjusts very fast (every 2016 blocks or ~14 days) and you could have transaction speed disruptions. If a block doesn't solve in 10 minutes but instead an hour, you'll have a lot of very unhappy people waiting for transactions to seal and they'll abandon the network after selling off their assets. That's just the time aspect, you mention the transaction fee aspect, and that will drive people away as well if they start to creep near what legacy financial systems charge. The declining block reward in BitCoin guarantees that transaction fees will increase because of the limited capacity of the consensus network's data-storage/transaction block.