In a prior life, I did a business case for launching a branded preloaded card. The primary business case is the same as travelers checks, namely that you are selling a currency for someone to spend in the future. This creates a huge "float" that the company can borrow against.
(If 1 million people buy $100 of prepaid, you have $100 million in the bank held in trust that can be used as collateral.)
The secret is that you have to be a trusted party for the consumers to buy your card. We attempted to sell the idea to Amex. The banks weren't interested because it competed with their other offerings. Starbucks immediately saw the potential and introduced their own.