Very interesting discussion.
I would be extremely interested in a +only training method if I could get one question answered. The current method strives to create a compulsion to do what we ask our retrievers to do, including working through different kinds of pressure. How will a +only training method address this issue? What happens if/when the + reward is not rewarding enough to overcome a distraction? What tools will be in the toolbox to address the issue?
I am open to this and I am asking a serious question, not seeking to dismiss +only training out of hand.