While I agree student loan debt may be unsustainable and start defaulting, I don't think it's as disastrous as the subprime crash because (from my understanding) most of student loan debt is on the books of the Federal government, and is not being monetized in anywhere near the magnitude that subprime mortgages were being sold on a global market.
The student loan situation is bubble-y, but one big difference is that the loans can't be discharged in bankruptcy. That makes the situation fundamentally different from most bubbles.
I'm not saying you're wrong per se, because I think the way student loans are heading is almost bound to be problematic, I just can't picture that bubble "bursting" like we usually think of it.
A couple outcomes I could think of would be a law making student loans dischargeable in bankruptcy again, a government bailout type program, or a law greatly reducing the availability of student loan debt. Any of those would have drastic consequences, but I'm still not sure it'd be right to call any of them a bursting bubble (except maybe the first).