MongoDB can already suggest useful indexes. Why not take the next step and allow MongoDB to autonomously create and manage indexes. Ideally it will automatically maintain the indexes over time as the structure and usage of the database changes.
You can go one step further. Why make people responsible for indexes when a machine can learn what indexes to apply and remove and do it?
Doing this will make the platform great at self optimising, and allow devs to focus more on build the app instead of optimising on the platform.