spectral rotation is possible!
after seeing the matt parker video on rotation by skewing, i thought what it would be like to apply this to spectral audio
link to that here ;    • Rotation without rotating.  

further points : you can achieve exactly a 90 degree rotation if you inversely match the automation of the frequency shifter to the sine sweep you generate. see this video for 90 degree rotations    • 90 degree rotations : further spectra...  

practicality? well who knows, you're the creator after all, use the tools however you like!
for me it was a little experiment, a bit of fun.
you could definitely use this for some sort of audio watermark that blends in nicely with whatever you're doing