I have more information obtained about the lounges.
As Mr. İlker Aycı ( Chairman of Board of TK )
The Business Lounge would is completely ready and would open with the movement. In a public statement he has also given some information about the Exclusive Lounge but didn't mention anything about eligibility to the lounge.
I don't have time to translate all these information at the moment. Link:
And I also have bad news for Elite Plus passengers. According to the Turkish Airlines website, this information has been changed recently.
Elite Plus passengers would be able to access the Miles&Smiles Lounge instead of the Business Lounge. The Business Lounge would only accept Business Class passengers on Turkish Airlines flights.
However, all the lounges are Star Gold lounges according to the signs at Istanbul Airport.
The copyright of the image below belong to myself.
