I decided to just go in and scribble something up for the fan duct. In my years of FFF printer upgrading, I've always dislike having to design them since they usually need to be more organic. To my surprise though, this duct came out better than I expected. It's effectively invisible from the front, giving the coaxial hotend assembly a very minimalistic and open look:

Design methodology

So I first decided that I was going to go back to the symmetrical-bolt mounting of the 6028 fans, and with the hotend holder now entirely made of metal, it can also help with heat dissipation. I then noticed that there'd be more space above than below the cooling 6028 so I pointed it upwards.

Then, similar to how I'd go about solving a maze, I started thinking up ideas on how the duct would start and end. I knew that the rear of the Coaxial8or was the most suitable location for the duct output. It also looked like a revolve would be beneficial to cool from multiple directions. I gladly found out that Fusion supports lofting from such a curved face:

I went on to refine the geometry so that it was at least 3mm or so from anything else and didn't stick out beyond the bottom wheel bolt: