We can achieve this easily as pointed below.
- Export tasks to Excel using Apps4.Pro Planner Manager
- With Apps4.Pro Gantt (Excel add-in) the exported tasks can be viewed in Gantt chart or edit from GUI which loads with in excel
- Even more this Excel can be shared with other users for review or set their preferences (by edit tasks)
- Now this Excel can be imported back to Planner with Apps4.Pro Planner Manager so all tasks will gets updated with the new details.
Boo - Yah!! Cool, this is really simple. Now you are tied with feathers to use Microsoft Planner the same way use have used Trello with external users collaboration.