The biggest potential problem with either of these approaches is simply the raw volume of voters on Stack Overflow.
The second-biggest potential problem would be the massive skew between upvotes and downvotes. When considering agreement or disagreement, this could be an issue.
The smaller potential problem... Is that it becomes even less enticing to actually participate here. Because there's no reputation, because voting is skewed toward SO, because the only people who have to participate here are rank newbies who can't post on any other meta... And employees.