Well, I know it is a freebie but the thread is for opinions here so I just tossed my two and a half cents into the fray!  :)
Actually there was an underarm prop made available for M2 years ago and made available on one of the Gay Poser sites as a freebie DL. I agree it should also be a standard with male models...at the very least.
I am not sure I understand what you mean as a rarity!?
The standard seems to be to add body hair to textures and not offering an option. I just want an option. The best way to offer that is remembering figures like V2/M2 (the only ones I am familiar with and am basing my argument on here...sorry) do have that optional and apparently often forgotten pubic hair and upper brow accessory.
Years ago some very creative texture maker offered through DAZ body texture set for V2. it offered several textures and tonal options which did not have pubic hair or upper brows painted on. They created various thick and thin brows/lashes/and transmaps for the pubic hair prop via Pose files to texture everything the way you wanted and the color you wanted. I loved it. I have modified these textures over time to get them the tone and color I want to use but the beauty of the set I will always appreciate as I continue using these is the option for the brows and lashes.
I think it was a more intelligent and versatile way to offer options....free or not!