We have completed the checklist feature as a solution for this.
Here is a related thread if you’d like to support or follow the suggestion for assigning checklist items: https://planner.uservoice.com/forums/330525-microsoft-planner-feedback-forum/suggestions/14924745-assign-checklist-item-to-specific-individuals
An error occurred while saving the commentBenoit C commented
I agree with many of the comments, I think the checklist is far from enough:
-checklist is limited to 20 items
-sometimes a sub-task should also contain other sub-tasks ... and the completion of the main task depends on the completion of all other sub-tasks ...