I had a former boss (a couple decades ago) that was also fond of the "open the kimono" saying. Ugh. WTF is wrong with saying "full openness" or "full disclosure" or something else that sounds appropriately business-like.

"Baring it all" would be a native idiom preserving even the emphatic nudity reference while not suggesting that you're taking off some other woman's clothes.

This is surprising to me too, in that what I know about "kimonos" is that they are women's clothing underneath which no underwear is worn.

What's the term supposed to refer to?

It’s a metaphor for showing someone things that are typically kept hidden.

Sure, but in that case... why not "lifting up the skirt"?

That characterization would be too graphic for many corporate environments.