It's a fascinating phrase, perhaps not least because nobody knows where it comes from but somehow people also seem to know that it's innocuous or know that it's sexist.
> Steve Jobs, the founder of Apple, notably used the expression in 1979 during a visit to Xerox Parc. He reportedly said: “Look, I will let you invest a million dollars in Apple if you will sort of open the kimono on Xerox Parc.” This memorable expression and meeting apparently led to him discovering the mouse, and Apple subsequently launching the first commercial mouse. [1]
In that context it seems fine to me. He's talking about a product. Now, clearly, "open the kimono" means to bare something naked. If you ask a person to be more "open kimono" as a way of asking them to be more open, I think that crosses a line. And, maybe if you suggest someone go "open kimono" on their work, that could be received offensively while not being intended that way. So, context matters. I'd probably steer clear of it entirely though.
Agreed, it's a bizarre phrase probably best left unused.