Even if all the formatters quit the project tomorrow, Wikipedia would still be immensely valuable. For the most part, people read Wikipedia because it has the information they need, not because it has a consistent look. It certainly wouldn’t be as nice without one, but the people who (like me) care about such things would probably step up to take the place of those who had left. The formatters aid the contributors, not the other way around.
Wales is right about one thing, though. This fact does have enormous policy implications. If Wikipedia is written by occasional contributors, then growing it requires making it easier and more rewarding to contribute occasionally. Instead of trying to squeeze more work out of those who spend their life on Wikipedia, we need to broaden the base of those who contribute just a little bit.
Unfortunately, precisely because such people are only occasional contributors, their opinions aren’t heard by the current Wikipedia process. They don’t get involved in policy debates, they don’t go to meetups, and they don’t hang out with Jimbo Wales.