Some good news after all
After removing all remaining license issues regarding missing copyright statements or license statements in some files virtualbox is finally in debian unstable. Since I needed the statements in these files and cause of some bugfixes debian ships now an svn version.
So this big and important piece of software is now finally official available.
To integrate virtualbox in debian I had to remove some sourcecode and therefore virtualbox doesn't contain the Guest Additions (they contain non-free code from e.g Microsoft). The good news here are that in the next version of virtualbox these Guest Additions will be available from the website and can be downloaded automatically with virtualbox.
Enjoy it! 
Thanks to feivel, who sponsored me 