AP Photo/Paul Sakuma A poster advertising GMAC services is posted at a GM/Chrysler dealership in Oakland, California. W hen you need a new mortgage in the future, will your only options be AmazonWellsFargo or AppleChase? The prospect of a mash-up of banking and commerce keeps people like George Washington University law professor Arthur Wilmarth up at night. “This would mean an end to healthy innovation and startups and competition,” said Wilmarth. “I think it is that dire.” Wilmarth sees the seeds of a new era of conglomerates in a series of actions by federal regulators and small firms to allow “fintech,” or financial technology companies, to become FDIC-insured banks. In June, SoFi, which offers student loan refinancing and wealth management services for high-income young people, applied for an “industrial loan company” charter in Utah, and early this month, the payment processing company Square followed suit . The Utah loophole has long been a back door for banks to get into...