Walmart has been trying to get into banking in the U.S for a number of years. They have had to deal with a lot of regulatory hurdles. They already have banking operations in Mexico and Canada. If Walmart is having a hard time getting past the regulators to disrupt this space, it's probably much harder for a startup.
Not really. Walmart's difficulties are because it's a real business. Typically, non-banking entities are not allowed to own banking entities. There are some very good reasons for this, primarily that if the non-banking entity struggles they have a very good incentive to raid the piggybank and/or take it down with them. After the past couple years it is easy to forget that banks are supposed to be more stable and less risky than other industries.
Clarification: Walmart's difficulties are unrelated to a banking startup's difficulties.
http://www.americanbanker.com/usb_issues/120_9/wal-mart-gets...
http://www.washingtonpost.com/wp-dyn/content/article/2006/04...