I don't think we need to 'redirect' anything. I think doing so is a bad idea.
Perhaps we could move and for a period of a few months or so, have all redirected articles from www. to en. give an automatic message suggesting that the bookmark be changed.
I see no reason to ever force people to change bookmarks. We support the past URLs, but we encourage the new URLs. We don't need to redirect or force bookmark changes or EVER break links in this way.
It's very easy to have www.wikipedia.com/wiki/Thomas_Jefferson and www.wikipedia.org/wiki/Thomas_Jefferson and en.wikipedia.org/wiki/Thomas_Jefferson all say the same thing.
--Jimbo