“There aren’t many directors who would feel equally at home staging the nostalgic ABBA songfest Mamma Mia! as well as the futurist opera based on Margaret Atwood’s The Handmaid’s Tale.” In fact, crossing between the worlds of opera and musical theater at all tends to be frowned on, but somehow, director Phyllida Lloyd seems to have won over the finicky devotees of each. Having engineered the current Toronto production of Handmaid, her next project is the English National Opera’s Ring Cycle.