Most “shrewd” trainers would hate the idea of exposing their potential National horses as early as December. They’d rather finish beaten 80 lengths plus in a John Durkan.
Good. That’s exactly what’s needed.
What I’d fear is one who is not good enough to win a modern Grand National, but ‘handled correctly’ could easily win in December. Maybe keep them out with a qualifier set around ‘number of handicap chase runs’.