As I'm considering buying the new Premiere Elements I was wondering if the latest version is capable of exporting my timeline to a XML-file, so for example one of my friends who doesn't own Premiere Elements but doés own Final Cut of Premiere PRO can work on my 'Elements timeline. '
As to your question "XML export in latest Elements?" - No.
At this moment, Premiere Elements 12/12.1 is the current version. Adobe is expected to release a new version at the end of September 2014. No one but Adobe knows the feature set for the new version. And, that type of information is not released until the moment of release of the new version.
You could always file an Adobe Feature Request Bug Report Form.
From my perspective, that is a long term type solution.