Seems like it should be possible to set up WordPress on your iSeries – in the IFS, of course. It is free, open source and easy to set up. Of course, for that you’ll need PHP and MySQL. Also Free. WordPress is a PHP app and uses MySQL as a database.
Do a Google search for “MySQL on iSeries” – or “MySQL on i5OS” – I’ve seen at least one example of how to install MySQL 5. Also, I believe that the iSeries is a supported platform for PHP.
If you want to play around with it all before you try loading it on your iSeries and you have a spare Windows box – download and install XAMPP and then download and install WordPress.
And let us know if it all works!