For years, world leaders have been trying to launch a historic overhaul of global tax rules, aiming to tackle an unwieldy system rife with loopholes long exploited by big business. That goal may finally be in sight.For years, world leaders have been trying to launch a historic overhaul of global tax rules, aiming to tackle an unwieldy system rife with loopholes long exploited by big business. That goal may finally be in sight.