THEY FINALLY DID IT: https://www.printables.com/model/887071-nv-aa1-12-airflow-amplifier
Optimized for 0.6mm line width (thinnest wall is 1.2mm). Recommended layer height is 0.2mm but lower is certainly possible if you have the time and want the smoothest surface possible. A small amount of support is needed for the screw holes, because these have an empty space beneath them to facilitate the Noctua anti-vibration mounts.
I made this model over a year ago and tried to get the dimensions as close as possible. This was difficult because I only had pictures as a reference and no measurements (except the size of the 120mm fan). The model has two round nubs on the sides as a way to mount it. I didn't design any kind of base for it though, so you'll have to make something or edit the model to make your own mounting solution. I only made this to see how well it would work and it works pretty well (tested with the NF-A12x25 fan it was designed for). The AAS can be secured to a 120mm fan using screws or anti-vibration mounts. I left the middle open so you can look at the pretty sticker that's on the fan.
Sources used for designing this model:
Noctua Desk Fan coming Q4 2021 - New 2021 Roadmap | HardwareZone Forums
Noctua quiere que uses sus ventiladores para refrescarte con su módulo AAS
Noctua Desk Fan Goodness... Powered By NF-A12x25 - YouTube
More & Better Cooling From Noctua And Even A Desk Fan | Computex 2018 - YouTube
The author marked this model as their own original creation.