On a practical level how would you prevent people from seeking a second job in order to pay their inflated rent?

Fixing the housing supply problem appears to be critical here. Without increasing supply, folks might find ways to work around the "mandate" out of sheer necessity.

Also I think the OP should broaden the question to read "lifelong contributors." The learning is a very important component of this, but broadly construed, that learning should include the practical experience gained from contributing to all sorts endeavors that produce social value. One of the critical problems with today's workforce is that so much of the work revolves around what social anthropologist David Graeber calls "Bullshit Jobs."

There's often very little to learn in these environments except how to play office politics more astutely ... the next time around.