It sounds like you've looked into this before, so I'll ask you: what is the use-case for per-user environment variables that can't be achieved trivially through ~/.bashrc or /etc/profile ?

It sounds to me like the problem they want to solve is that there is some piece of information which needs to be present in the environment for every process that a user runs regardless of the context it was executed from (eg. DBUS_SESSION_BUS_ADDRESS)?

In which case it would surely be served better by being contained in a config file in a standard location where it can be read by every process that needs that info instead of the executing process having to know the information and pass it in the environment, for every possible caller and calling context.