It's been a couple of weeks since we posted, so we thought it'd be good to do some housekeeping. The next class pack will focus on the Sniper. It's actually shaping up to be the largest TF2 update yet, with multiple new maps and a bunch of gameplay tweaks. In addition, we've got another update in the works that should be done before the Sniper, and that one will include some new content for all classes.
As we can see, the next class pack will be the sniper, but all the classes will be getting new content before that comes out, as well as "multiple new maps".
Read the update on the Official TF2 Blog.