Is there a way to estimate overall team planned load before assigning tasks to specific people?

Hi everyone,

The use case is as following:

Project managers just want to assign new tasks to some team(add it to team's backlog) and then team lead will take care of it and assign tasks at some later point. In this case backlog can have several tasks already with planned dates and hours and eat let's say 50% of total team capacity for the next week but resource planned won't show this as those tasks are still in unassigned state and are not reflected in workload stats.

Is there some way to calculate both total available(not allocated) team capacity for some specific period and total planned hours(from unassigned tasks) for the same period and show them on report?