While i do disagree with the above points, at least someone stepped up and addressed the issues. The mercy rule will never happen, and if it begins to gain momentum, i hope it is enacted long after my coaching career is finished.
As i think about more, substitutions at the college level are unlimited. If you are considering limiting subs, then consider the college rule-- there are unlimited subs in the first half but once a player comes out, they cannot re-enter. There are unlimited subs at half time. In the second half, a player is allowed to come out and re-enter once.
Personally, i do not think that sub limits of any kind have any place in high school soccer. I think the substitution strategy is part of what makes high school soccer so much fun. Also, this topic was originally brought up b/c one person was concerned that less skilled players were only playing 5-10 minutes per game. If you limit subs to any degree, then those players will begin to receive no playing time at all. Then, that same person will be arguing that players are put on the team to simply "fill the roster".