I'm not sure it really will change anything. The assumption is that people with IE6 chose it and can change it which is often not the case (corporate users with a strict IE6 policy notably).
It's reasonable to expect that your users will stay, and the browser repartition will follow the same curves it did before.
That is a possibility for sure. Since pb is a younger audience my gut feel is that there are a lot of users who are simply clueless about what browser they are using and just don't know better. Whether they do anything about is another story.
Well, this is 2011. That sort of policy just isn't in application anymore. Because companies with policies are companies with upgrade policies as well.
Make a website (IE6 Compatible, of course) that explains in tedious detail all the reasons a corporation should upgrade. There are real security issues that they should care about. Put this in the form of a white paper, but you get to put a few ads for corporate IT stuff in the corner.
Have a prominent "mail this to my IT administrator" link, that people can click, which mails a link to the page to an email address provided by the user. Use a mailto: link, so the email comes from inside the network, as they're going to get a lot of these, and we don't want them blocking them.
In the footer, have a link to your "developer page" with the text, "Help us educate corporate IT to IE6 security risks". On that developer page, have some javascript that people can cut and paste into their websites that senses when a browser is IE6, and if so, puts up a warning box with a link to the white paper page.
Now you have a potentially viral spread. You have an easy way for developers to alert their users to their browsers vulnerabilities, and do it in a way that leads those users on a path that might actually actuate change, which is, alerting their IT people. When it gets to the IT people, you have made a strong technical case that they can use to go to their bosses and get things done.
Plus, you might get a few clicks from IT guys on your ads to pay for your server space.
It's reasonable to expect that your users will stay, and the browser repartition will follow the same curves it did before.