Was at IST today and there was a Kalitta air 747 (cargo).

Re: TK's fleet plans, IMHO the 747-8 and A380 can make sense at highly slot constrained, high volume airports. If anything, old Atatürk would fit that bill - but it could hardly handle the significant extra pax flow from several such birds being based there (vs. visiting from e.g. DXB 1x per day). And it will close eventually.

If the new IST airport will be everything it is said to, then it should have much less capacity constraints, which in turn would lessen the need for the big whales and would suggest going with B777X or A350-900 /1000 instead.