Mega-banks are feeling pressure from shareholders and the public in ways that seemed unlikely even a few weeks ago. At JPMorgan Chase, directors and managers face the very real prospect that shareholders will vote to strip chairman and chief executive Jamie Dimon of his board oversight role after a leading advisory firm charged the company with “material failures of stewardship and oversight.” In Charlotte, N.C., protestors planned large-scale events outside Bank of America’s annual meeting in the sort of public display that could push the biggest banks into making the sorts of changes that governance scolds have long demanded.