I didn't see this in the thread.....
At least one computer fan mfr makes "sawtooth" blades - really, staggered notches..... But the claim is for noise reduction....
Noctua.at - sound-optimised premium components "Designed in Austria"!
They do also claim higher efficiency..... But, it's not a uniform notch - each successive blade has a slightly different offset from the last. So cross application is questionable.
Of course, we could very well be dealing with different Reynolds numbers etc. etc.
With respect to the Dreamliner nacelles.... So the claim too is to reduce noise.... It takes energy to make noise - energy that doesn't make you go forward... But the sawtooth allegedly breaks up larger vorticies... So to do that, I suspect it takes energy. If you use energy to cancel out other acoustical energy - I imagine there's a penalty. Think of luxury car acoustical noise cancellation or noise canceling headphones - it costs power to do it, but you'll experience less noise. This is just intuition speaking here
The accuracy of that is all up for discussion.
I guess it's worth mentioning the very strict noise regulations for aircraft taking off
------
Personally, rather than playing with funky edges/passive control - I'd like to see more research and testing on active flow control. Hyundai apparently has a cool feature in one of their cars that scoops air from under the car and blows it out small vents (at higher velocity) in the tail lights to combat the intersecting surface flow shenanigans back there... Aptera dumps their exhaust out the tail in a similar fashion too for related reasons....