I remember someone suggesting this before, but we didn't want to because then some of the skins might be confusing.
OK, but having two characters with the same skin can be confusing too. Maybe add the six least confusing skins of each race/class combination. Then you can make sure there are never two characters with the same skin in a match.
Some of the skins are already terribly confusing. That reminds me. I've been meaning to post some feedback about this... ~adds to To Do List~
I find many skins to be confusing. Sometimes I can't even tell whether it's a warrior, priest or wizard That's why I'm always happy when people don't use skins in ranked games