I may be wrong, but my understanding is that (at least for the student loans I have), the owner of the debt is allowed to garnish my wages (and I have heard even social security payouts) after some amount of time in default. So I think your plan would only work for people who are willing to be unemployed indefinitely.
Sounds like a scary criteria to an entrepreneur ("you can never work!") but it might ultimately make sense for those who go to university, but end up marrying someone with a good job and becoming a lifetime dependent of them (in est, the classical homemaker.)
There are probably a few other less-common situations as well, where a person has no money of their own but access to plenty of the money of others, e.g. the "trust-fund baby."
