I've never once seen anyone make use of the two small holes on the sides of the newer AirPods cases.
Discussion

Wow! Do you tie it to stuff? Just let the string dangle? Please elaborate
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRLk861IwbgrO3v3hwWRpRHkGLaIx0nmCwPGQ&s
Just a lanyard to play around.
Guess that counts. Had to get a newer pair recently and was looking at the useless holes wondering if they will keep them in next gen. I'm extra annoyed likely because I had to buy them a month or two before they likely release newer ones