I think making formal rules saying that you may not win the regional chairmans two years in a row is unfair. It would encourage the most effective and powerful teams to slow or stop their work for an entire season and this would not be beneficial to the FIRST community.
However after winning a regional chairmans maybe next year that team should have to submit to another regional. Short of the regional in Israel...most of the time the regional chairman's winner is a team that attends multiple regionals or one that easily has the ability to. Moving to a different regional gives teams from the local regional a new chance at the award and also gives the winning team a chance to compete. Besides...it is always exciting to see a new face at regionals.
