Sounds like nothing more than a calculation provided for the borrowers convince, but actually serves no real purpose. You might look at actually providing a hedge to protect from a rising bitcoin value against fiat for an added fee by buying calls.
Please, read the OP again.
If you borrow 10 bitcoins today, to pay next month, you will theoretically pay aprox. USD $300.
Now suppose that in 10 days the bitcoin price jumps to USD$ 1000.00 per bitcoin, you still need to pay 10 bitcoins back, but now you will need USD$ 10,000.00 to buy 10 bitcoins!
But why value does it add? I agree you used the wrong word calling it a hedge, but other than informational value, I am missing what it provides.
From the OP:
You borrow 30.0 BTC today, to pay next month, suppose BTC is at USD$30.00.
Next month you will make the payment, BTC price is now USD$ 60, instead of paying 30 BTC back, you will pay 15 BTC, the amount in MtGox USD remains constant.
Simply put, you are getting a loan based on the value of USD (or whatever currency) but paying in BTC. If you borrow $300 of BTC at 10% you pay back in $330 of BTC. Instead of the number of BTC at payback being determined, the value of the BTC is. If BTC rises significantly durign the loan period, you may end up owing less BTC than you borrowed. OTOH, if it falls a lot you may owe 2x or 3x as much BTC.
Whatever one wants to call it, such a loan is exactly equivalent to a USD loan, but with the funds delivered and returned in BTC.