How high can the transaction fees become?

[philipma1957]

Look at the fee spikes of the past and double or tripple that to get some idea of how high they can get in the coming years. If Bitcoin shoots up, the traders will have more value in their hands and they will be able to tolerate higher fees when they move coins in/out/between exchanges. But the good news is that spikes don't last for long, just a few weeks and then fees go down to a more manageable level.

300 to 500 usd would be pushing what people would pay in most cases.