I think some minor differences in BTC prices may remain only because of normal trading activity and the cost / complexity of moving the currency between exchanges to take advantage of arbitrage opportunities.
This may be due to differences in demand for BTC between various countries and regions, depending on the population of traders who use each particular exchange. The difference in BTC values ​​should not be too large, or exist for a long time because in the end people will see the opportunity for arbitration to develop and use it, after that the difference in price between exchanges must decrease.