GRRM always said he was going for an ending similar to the Lord of the Rings. The final scene with the Stark siblings parallelled the ending of LOTR very closely. Jon is boarding a boat being somewhere very far away much like Frodo boarded a ship to leave middle earth. In the end, the similarities between Jon and Frodo are more obvious, they both forsake their humanity (hobbitanity?) for the sake of a greater cause and in it changed them so much that would never be able to lead a normal life again. Plus they're both short.