As Avenan alludes to in his link, this "keyholing" was used on the hubs (usualy Maxi-Car) on French randonneuring bikes in years past. I know that some Alex Singers featured these hubs, and I believe they were also seen on the bikes of Rene Herse.

I would think that this treatment would weaken the flanges and lead to increased failures, but I have no experience with them whatsoever.