Is it possible to dump the entire contents of a PST file to a portable (preferrably text) format like XML?
XML is unlikely – most programs use mbox, Maildir, vCard, LDIF, iCal – however, these are formats that are far more common and portable than XML for mail, calendars or contacts.
The libpst package comes with a few tools:
Unfortunately, its output is lacking some data (especially in case of journal entries), and it does not extract tasks or notes.
However, Outlook itself can export any folder in the PST as a CSV (comma-separated) file, containing every single field.