walmit:
I appreciate that language is not static but is this phrase a worthwhile development that should be kept and used?
IMHO yes, it should, because it's commonly used in the spankophile community, especially the spanking-oriented reading and writing part of it (which includes us Library members) and to me it's a bit of a 'turn-on' to read (and write) that phrase as part of the descriptive dialogue.
Obviously, a word referring to the human buttocks (bottom, behind, seat, posterior, derriere, etc.) is implied after the word "bare," but AFAIK the expression is used almost exclusively in dealing with spanking so the description of the specific target area isn't always necessary: "She got it good and hard, right on the bare." "Young man, when I get you home you're getting paddled on the bare!" "Do you think she'll really spank us on the bare in front of your sisters?"
AFAIC the expression "on the bare" gives a bit of relief from overusing "bare bottom," which I'd opine is a highly exciting term but still can be repeated a bit too much in a spanking account.
"Show him (or her) that you really care, spank him (or her) soundly on the bare."
Well, I like it anyway

... --C.K.