Moving people to fullback has been an obsession for a bit. It used to be promising young halves (See Tomkins/Lomax) and more recently especially in the NRL it’s been the best athlete in the team. This has partly been lead by players over there because fullback is seen as a more valuable role than say centre or wing and therefore attracts better contracts. It’s also seen as more of a glamour role.
But no I don’t think Macdonald would go well at fullback.