> do you pluralize that as iPhone Xs even through that's the new model?

I'd have to go digging, but there was a Twitter thread in which I participated about this that Phil Schiller chimed in on. Apple's official(?) stance is that you never pluralize iPhone; instead, you use the word "devices".

"A friend and his wife both have iPhone X devices" (or, more likely, "A friend and his wife both own the iPhone X").