The associated freak-out would be deep and wide enough to motivate them to be more secretive, rather than more sharing, unless they are with someone with whom they feel a great deal of trust and share an emotional bond.

I can agree with that, I think. I've criticised genderfuck stories before for being too flippant about the pain of gender dysphoric feelings associated with not belonging in one's body, so it would be kind of hypocritical not to! I do wonder if just the fact of sharing that same utterly bizarre experience would become enough to create a bond where one hadn't existed before, though, had it happened to a different set of characters.

On the other hand, I do think that given the story's emphasis on the sexual, sensual aspects of finding yourself in a new body, there is an argument to be made for the desire to try out the new bits with another person being strong too – a willingness to perceive sex as physical more than the specifically intimate experience you're framing it as, which also goes along with the way straight men are culturally supposed to perceive sex.