A satellite up-link would certainly complement the existing Black Boxes and whilst I doubt it will replace them (connections drop out etc.) it would certainly allow a) greater accuracy in wreckage finding b) access to some/all data without *having* to retrieve the boxes c) recording of additional parameters such as video (as ExXB suggested). Many planes now have cameras in the tail, on the belly (A380, A350...) they might be able to provide additional data or show an object (drone!?) that happened to be ingested into an engine, for example.