Thanks for your suggestion, but I have to disagree.
As is the nature of Code Reviews, each one of them is done on a case by case basis so we are already pushing the borders of Stack Exchange Q&A system (on other sites, most of our questions would be seen as too localized).
That said, I think of our site as a collection of useful case studies that others can learn from.
The about page puts it like this:
With your help, we're working together to build a library of detailed code reviews.
Once question length increases about a certain point, two problems stand in the way of this goal:
Reviewers are put off because they don't have the time or energy to review vast walls of code. This contributes to our already below average answer ratio of 1.9
The same thing happens for visitors only it's worse, because now they're facing a huge question and possibly several huge answers, which requires too much time and effort to learn anything from the whole endeavor.
Also keep in mind that good code reviews in real day-to-day scenarios are done at check-in. This implies that the code to review forms one logical unit (e.g. a feature or a class) and is not overly long.
Code Review should focus on providing concise case studies. These case studies should focus on a particular feature or class rather than entire projects (or large parts of them). Increasing the character limit is not helpful as it would worsen, rather than improve, the site.