As you may know, Trac has been set up to manage planned functionality for 2.0, and can be found at http://sourceforge.net/apps/trac/usebb/wiki.
Because I fear a lack of time in certain weeks and to keep the 2.0 goal feasible within a decent time, I postponed the features that were previously marked for 2.0.0 alpha 3 to 2.1.0. This includes: polls, threaded topics, private messages, attachments, etc. More features may be postponed in the future eventually.
So 2.0 will be a basic functional release with (at this time) still 2 planned alpha releases. "2.0.0 final" will be at least equal to 1.0 in functionality, ofcourse with the huge code rewrite, modules, tagging, etc. 2.1.0 will be the extended version with (optional!) modules for the features described above.
I must also remind people to the fact that more tickets may be submitted to Trac. These can be discussed and set to a milestone for some future release. See http://sourceforge.net/apps/trac/usebb/report