There are no new key features. 4.0 will work on joomla 1.5 with out legacy mode. That is the idea. After 4.0 is ready then we will move slowly to the MVC pattern and start adding new features (check wishlist).
When will it be ready? As I wrote here:
http://compojoom.com/index.php/forum.html?func=view&catid=2&id=540#540
we will need around 80hours to get it done. That is a lot of time and we all have another things that have priority over !jocomment. As you wrote - it will be ready when it is done
If you want to speed the process - well you can do one thing and that is donate
(scroll to the bottom of that page)
Greetings!