This is one of those situations where I'm grateful that I'm such a noob.
When Chris explained this passage to me a while back at a different forum, I understood it as the Buddha was telling people how things were going to go. And she reminded me how many births we have in different forms. We already know that Maitreya will come here in male form, so I just said, "okay, cool." One thing I considered is, a logical reason that a female can't become a sammasambuddha is because of the condition of outer society, not a female's inner condition. From everything I've read in this thread it doesn't seem that the Buddha gave a lot of detail to explain what he said.
Like I said, being a noob sometimes makes it easier I think