It's not exactly what you're looking for...
But you potentially could use the "Login Redirect" add-on to accomplish this:http://www.concrete5.org/marketplace/addons/login-attribute-redirec...

If you're adding a brand new attribute, it's reasonable to say that your userbase does not already have it - so you can do a "redirect on next login only" redirect that take them to their profile / other form /etc. where you ask them to update their profile for accuracy.

It could even be a single page / overlay etc that asks them to subscribe to your newsletter - which when submitted updates their user account with that attribute value.

Anyhow, that's a possibility you should explore to see if it meets your needs.

That being said, I like this add-on idea.

This would work if the user was not already logged in. But they are \)

So, would you be interested in writing the addon?


Let me know


Kev

One other possibility:http://www.concrete5.org/marketplace/addons/auto-logout/...

Unfortunately I cannot commit to additional development jobs at this time. You might reach out directly to some of the major players in the forums and/or post in the Linked-In group if you don't get a response here.

I can add a required user attribute for you.