Gendry. In the show, he’s still rowing his boat. In the books, he was with the Brotherhood as a smithy.
My dream would be for Sam to go to Oldtown (as he does in the book), find an ancient text about forging Valaryian Steel, link up with Gendry (who apprenticed under the only man who could manipulate VS), and start mass-producing the Walker-slaying weaponry.
Long-shot, but it’d be cool.
It would be cool!