There are also multiple efforts to change the ways Linux distros themselves are structured to help differentiate user-focused applications like Firefox or Chrome from the core OS, as well as making it easier to have per-user configurations of platforms like Python. Way too many things that could be handled completely at the per-user level (as they are on Android) currently require root access to the whole system.
Some interesting projects in this space (at varying degrees of maturity and popular uptake):