I really like this thought process. It becomes a civil right issue ( for the unborn human), therefore any state laws allowing the murder of the preborn would be unconstitutional, and you would not need a federal abortion law, which itself woukd violate the constitution. But this declaration of personhood would achieve the same thing.
There’s been an initiative writing this angle for quite awhile.
http://www.personhoodinitiative.com/about-personhood.html