There is no obligation to return the current market value. To make you whole, you would get 8 back.

That's precisely what isn't happening; if it bankruptcy that would be the case, but civil rehabilitation is allowing some portion of the BTC to be returned.

That's why people are so excited about this news.

He used $8 to receive in exchange a certain amount of bitcoin. What he lost when Mtgox filed for bankruptcy was bitcoin, not USD. To make whole, shouldn't you receive what was lost?

That's not how bankruptcy works. He effectively made an unsecured, interest-free loan to Mt Gox for $8. The only thing he's entitled to in the event of default is that $8, what the company used his loan for is irrelevant.

I think OP meant he left $8 worth at the time of BTC in his account, not $8 USD.

It doesn't matter whether his $8 was in the form of BTC or not, all he did was make an $8 loan. Sure, the loan contract might have stated he could've accepted BTC instead of cash at withdrawel, but that's completely irrelevant once the loan issuer entered default. At that point OP is obliged to accept JPY as restitution, per the bankruptcy laws of the relevant jurisdiction.

Is there precedent to be repaid losses in line kind?