I have just checked with Oceania this week and was assured by a top level decision maker that Turkey is still very much of their upcoming itineraries. They had changed one port in Turkey to another, but have no plans to make any further changes. I also checked all the travel warnings on the government site and Turkey is not included. I was assured by Oceania that any mention of them changing their itineraries is not true. I would imagine that should security issues arise in the future they would have to make changes. I doubt they would leave anyone hanging if they had to change the port of embarkation or debarkation due to security issues.