Asking for 60% is a bit high.
I think it depends on the debt. I really don't think this will work with a one-size-fits-all rate for debt purchases. Otherwise, there's nothing to stop me from creating a fake account, lending it some bitcoin, claiming default and then on-selling the debt here for 20%.
Some debt is worth more than other debt!
Yes debt has different value. However, I was looking up debt collectors in the U.K. and they typically charge between 10%-20% depending on the difficulty. Granted, bitcoin debt it a unique animal, but I think if Kaos advertised a range or a maximum purchase price, he could make quite a bit of money. Especially with that DI debt.