I could be wrong but I think it might have a side effect of not being detectable either
I was watching the Thriller Bark arc recently and saw that scene where Absalom Kidnaps Nami in front of Usopp and Chopper and both of their scents seem to disappear. I can see Oda making Shiryu undetectable by haki and stuff. This could potentially lead to a nice little call back of Zoro learning to cut "nothing"
I'm definitely looking forward to it, especially more Shiryu action