It was until recently that declaring bankruptcy would be a big social stigma. Prior to recently declaring bankruptcy is something that many people would be ashamed of. Now, today, people tend to be proud of declaring bankruptcy. People are no longer ashamed of not following through with their promise to pay their debts as agreed.
The thing is that as of the day a student graduates college they will almost never have a job (they may have one lined up, but will have not started work yet). This would mean that students would likely not qualify for your "penalty". Also to say that someone has a "good job" or "good income prospects" is very subjective and would likely be found to be unconstitutionally vague and unenforceable.
Once upon a time when money was not fiat defaulting on a loan meant you had lost someone else's hard earned capital.
That was regarded as shameful and rightly so.
Personally I would never in a million years default on a peer to peer loan like a prosper loan regardless of my financial circumstances. Defaulting on such a loan is stealing from someone who worked and earned their money and is trying to earn a return lending it out.
It would not bother me at all, however, to default on a home mortgage. That money is in no way someones hard earned savings. The bank simply created it from nothing. In effect they are lending me stolen money and I have no problem defaulting on thieves.
People are proud to declare bankruptcy because they feel that they are screwing over a bunch of crooks. Truth be told they are largely correct in this judgement.
Regarding student loans the policy would have to be applied to all student loans for it to be effective.