The only risk I can see by defining an optional "spi" envelope is that the class can be segregated from the start or even have spis on all boats. If there is no room for a spi in the rules, it will be left to those who want to tinker and the class can decide later on when more boats are built. Then 'we' know what works and what is needed to thrill the young ones and keep them involved. Just my thoughts when I try to think strategically about the question.