Benjamin Forgey is wondering what exactly took the Kennedy Center so long to unveil the new plan to remake its architecturally embarrassing digs. But better late than never: “From opening day 31 years ago right up to the present, the big box on the Potomac has remained a huge urban faux pas — an outpost of culture separated from the city by a deep moat filled with speeding cars. The plan unveiled yesterday, conceived by architect Rafael Viñoly, does a lot to correct the mistakes.”