Hi Gianmarco,
It is on our road map to implement import/export for the blog but no one is working on it right at the moment, so if you would like to work on it that is possible. It will take a good deal of research to do it right. You will need to study the existing code for the blog and you will need to know about RSS format and/or BlogML, ideally we would be able to import and export from either format. Ideally you would implement it against the blog business objects not directly at the database level unless new methods are needed (because we support a lot of databases). Basically parsing the feed and then using business layer methods to create the content in mojoportal blog.
Also, the current blog comment system will be replaced with a new comment system later as described also on the road map. My plan was to wait until the new comment system is in place before implementing import/export since people will also want to import/export comments. But I leave it up to you if you want to implement import/export in the current blog comment system.
You would need to sign a contributor agreement and return it to me, and or if your employer owns copyright to work you produce then your employer must also sign it.
Best,
Joe