Would it really make sense? I think chances are from pretty low to zero. Türkiye clearly has chosen an independent path with TFX Kaan, Hürjet and Kizilelma. They would fill a possible fighter gap with other means than acquiring brand new KF-21 which could be restricted by US and UK.We can't get F35's, they are messing us around over old F16's, if the timing lines up it would make sense to buy these. But i suspect if the engines are american they will create problems to stop us from being able to purchase them.
From a pure technical point of view: TAI and KAI would make a great aerospace duo for overlapping offsets in a hypothetical Boramae deal. Both experienced in license building GE turbofan engines, integration of Turkish sub-systems and missiles on a Korean warplane would be hella interesting.