We're currently discussing whether it's possible to use the activities recorded in a Case (including the scheduled activities in a timeline), export them into Excel and convert it into a Gantt chart, but I can't see a way to export all activities associated with a Case. When I look at the options in the Civi Reports, it will only export the most recent activity. Would Drupal Views be any use?
Yes, you would be able to do that with Drupal Views. There is also an extension that provides the Case Activities with the API: https://civicrm.org/extensions/caseactivity-api