Now that you can manage tasks by project the ability to enter each team members capacity for a given week or sprint would be a great feature addition.

Then when the team member enters the project tasks with an estimated time there should be a team level kanban board to show all tasks for the given week or sprint organized in various ways (by team member, by week\sprint, by projects, by task lists, etc..).

There should then be a built in quick dashboard and view of the entire team and their current weeks\sprint capacity... plus or minus to show under or over allocation of resources. True team task and capacity planning