Christoph already wrote several blog posts about the upcoming projects plugin. In his last blog, he mentioned that a project can now be created on-the-fly by reading the git or subversion output: All the files under version control are automatically listed as files in the project.
However, this is restricted to git and subversion. If you always wanted to contribute to Kate, you can give other version control systems a try, such as Mercurial (command: hg manifest). Just quickly build Kate, and send us a patch!
Update (2013-10-31): Support was added in commit on 2013-03-02 and is available in KDE 4.10.5 and later versions.