The best we could hope for is a huge shift from SA-like license preference to merely BY-like license preference among the community. Highly unlikely.
Not just the community, everyone that has ever edited a Wikipedia article.
Perfectly acceptable would be a community effort by people who accept BY-like licenses to rewrite stuff from WP and our sources into Knol, under BY.
The question is whether that's worth it...
We could move small amounts across by persuading everyone that's edited a particular article to dual license their contributions to it under CC-BY and agree to give Google the more extensive rights, which is achievable for some articles (some small amounts could be rewritten, as you say). I don't see the point though. Why is having them on Knol a good thing when they're already on Wikipedia (it's not a bad thing, certainly, but I don't see that it's a good one)?