Yes, the K24 SPI communication is full duplex supported. There has specific register bit to configure in 3-wire mode.
See RM description as follows.
Typical master to slave connections are shown in the following figure.When a data transfer operation is performed, data is serially shifted a predetermined number of bit positions.Because the modules are linked, data is exchanged between the master and the slave. The data that was in the master shift register is now in the shift register of the slave, and vice versa.
So when you just use three wire, the POPR register is getting dummy data when its associated pin is floating.
This is from hardware perspective, the 3-wire is working. I am not quite sure if the SDK 2.4 support this feature or not, I will help to double check.