I wouldn't be surprised if the shape and packaging we think of today as a crossover is thought of in five years as an ordinary car -- and today's sedan will be the exclusive purview of tomorrow's fuddy-duddy and fleet owner. Buick Century will of course soldier on unchanged.
Sedans have been getting taller. They commonly have cargo passthroughs. Another generation and they'll all be packaged like Muranos -- carlike shapes stretched over SUVlike passenger/cargo compartments riding in carlike spaceframes with FWD/AWD drivetrains. I'm not convinced that's a bad thing.