A different twist on the hat debate...
My opinion is that the airline peak caps are a "Well and truly passed the use-by date" anachronism that should be consigned to the past and happily left there.
The only practical use for an airline cap that was suggested to me a few years back was as a receptacle for ones' wallet, keys, etc, when going through security.
My airline stipulates hearing protection, viz vest and our ASIC (security card) for when on the ramp.
Having said that, to suggest that an airline cap could become FOD is a bit of a long bow to draw, IMHO.
During my 40+ years of commercial flying and innumerable external checks, the peak of my cap has saved me on at least two occasions from a broken nose, or worse, by giving me a split second warning that I was walking into an unseen object or structure on the ramp at night.
With respect, that's not been my experience. I've had more dings when wearing caps (especially hard-hats) than when I've not worn them.