Multi user support is a mandatory first step for a thing that I find absolutely essential to any computers being used in a family environment: parental control
- being able to limit/block kids session time
- limit/monitor program access
- limit/monitor internet access
- prevent installation of unwanted programs/accelerants/add-ons
Simply implementing separate partitions will not cover this requirement, and separate partitions are still accessible so there is nothing preventing my younger kid to mess with my eldest homework, or my kids messing my administrative documents (apart from implementing password restricted access, encryption, but it will quickly turn out that once you have implemented these functionalities, you are actually very close to multi-user support).
That being said, for your use case maybe it could be possible to have the option to automatically open a session if only one user is available on the system?