I am surprised that posters on here are so "vanilla" !
Obviously, I am not a jock
but I once chatted online with a guy who asked me if I would be willing to sell him a pair of my old sneakers. He also told me he actually talks to boys on the street to buy their sneakers (this way he enjoys the **freshest** smell). Countless guys asked me for a photo of my feet/socks/sneakers
Honestly from what I see on gay chatrooms/apps, guys who have a fetish for sweaty socks, smelly sneakers or dirty underwear are far from being uncommon.
I am French, and I can tell you that French gay slang even has a word for guys with a sneakers/socks fetish ("kiffeur")
In my opinion there would definitely be a market for smelly socks or briefs.