Task re-assignment to a group has worked in Windchill Foundation, but this feature has been removed because of performance issues (SPR2039591).
PTC support mentioned: When a task was reassigned to a group in Foundation, the ownership of the task was shared by the group. When displaying a user's worklist, all the tasks owned by the user were displayed and then a check was made if the user was a member of any group which was assigned a task. The latter created a performance nightmare since it required a time consuming search of groups, group membership and tasks.
Why not enabling a functionality of re-assigning tasks to a bunch of people using the same behaviour as is used when a new task-instance is initially assigned to the people given in a specific role (participants)?