Even if they fly to AU, one issue to consider is that the IST - Europe leg will likely be on a narrowbody or a short-haul configured aircraft.
This is a deal breaker for me unless prices are extremely good to make up for this or I want a stopover in Turkey. Whether the general population will care is another story.
General population usually wouldn’t care as much. But that aside, the whole point of would be to offer a wider range of single stop destinations, many of which wouldn’t be available on wide body anyway. And a lot of these in the 1-2 hr flying range of IST so narrow body being Ok for shorter fights. Even QR has quite a few narrow body services into secondary Europe ports, with longer flights than you would see on TK.
A bit like SYD-DFW, which transfers to predominantly AA narrow bodies.