ive always thought genderfluid june/john makes more sense
breath is about freedom, direction, change, etc. and well junes an heir, who inherit their aspect. (plus callie called her the embodiment of freedom)
it makes more sense that that would be the case, especially if june is an ultself, since why should he have to be confined a binary when she's gone beyond that??
i also think it works well for him as a character. she probably need to wrap their head around it a bit but john, in my mind at least (i will admit i may be forgetting parts of their character here or getting it wrong, my memory is not great at times), has always been flexible and able to adapt. the problem for him is finding the direction she wants to go in, but once they do they thrive. i prefer the idea of john realising they dont have to conform (gnc june my beloved), that his expression can move and change.
i do kinda realise this veers a bit on the "john and june being seperate" party who just don't want a trans woman in their media due to bigotry but i feel like this fits in her narrative and i like it as characterisation.
i am now realising a good portion of my gender headcanons fall into some form of gnc or genderfluidity. as a certain seer would say, Projection perhaps?