I don't think the short seller is a lender/borrower.
The current BitAssets are bit like a contract for difference so it's just a market that matches buyers and sellers.
It is a contract for difference, but you still need to borrow bitAsset to create it into existence. It becomes your liability, aka debt.
If the shorts were extremely bullish they'd be wiling to pay a premium to longs to take the other side of the contract and vice versa.
I don't know though.
This is true. Saying that shorts should not pay premium, I was not correct. They may agree to pay under certain conditions.