This is fantastic! I'm a huge fan of fic that addresses the intercultural issues and power balances of the Potterverse, and this is so very well-done. Your choice of characters is inspired -- Neville as the one who has the sword, not deliberately ill-willing but attached to his view on the matter (perhaps as much for convenience as for tradition), Filius as the go-between who has denied part of his heritage to fit in with the wizarding world, and then of course that excellent portrayal of Griphook.
The pairing has never occurred to me, but it makes so much sense.