I've been pondering this myself, and my two thoughts on the split were at either Ron's return, or just after Malfor Manor. But I think what you say about the Xeno thing is a really good point - that gives us an explanation of the Hallows right at the end, and Ron the dramatic climax of the first one.
...I wonder if we'll get a post-credits sequence. (I suspect the Epilogue might end up post-credits in Movie 2)
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...I wonder if we'll get a post-credits sequence. (I suspect the Epilogue might end up post-credits in Movie 2)