Museum building projects always spark a visitor boom, as people want to see the new spaces. But if attendance drop-off is too dramatic when the excitement wears off, a museum can fall into crisis. MFA leaders project they will double their usual attendance after the wing’s November opening. (Typical attendance is 60,000 to 80,000 a month in the winter, says Kimberly French, the museum’s deputy director of communications.) How will the MFA sustain the crowds? French believes an April show featuring work by glass artist Dale Chihuly should do for the MFA what Shepard Fairey did for the Institute of Contemporary Art in 2009: draw visitors even after the thrill of the opening has worn off.