The main thing that drives training for the high performance biplanes is the insurance companies. If you're willing to forgo the insurance coverage you can get a few hours in a Citabria and then go blast off in an S-1. It probably won't end well but you are 'legal' to do so. I wonder how you could create a regulation that would cover that loophole? When I started flying these airplanes there was no formal spin training. I experienced inverted flat spins but not the entire list of possible Pitts spin modes. You did that on your own over time (often by accident) and with reasonable altitude.