Integration between MS apps - common data model
Quite a few ideas here are around integration between Planner and other Microsoft applications. It strikes me that one way to achieve this is for MS to establish a common data model that it's various applications can access and present out to users. While in this case its tasks, the same could also apply to other common objects like contacts, groups etc.
For tasks, there are fairly well established models that could followed, whether that be agile focused (e.g. Task> Backlog> Story> Feature> Capability> Epic) or more traditional (Task> Project> Program> Portfolio).
If there was a common model used for these that all MS apps could call on, for a single bit of 'work' individuals could use what ever tool they want to know what their workload is - Outlook, Wunderlist, Planner, Visual Studio. Team Leads or project managers can use tools more suited for their role to monitor teams progress - Project, Planner, etc. and so on.
Clearly that's potentially a huge engineering effort, but I think that sort of architecture would give MS a huge amount of flexibility in the delivery of tools and interfaces, and give us end users a much more consistent and productive workplace.