Google plus rolled out its cover photo dimensions to max of 2120x1192px. It has also added some new features for redesigned the timeline. Google+ Product Manager +Sara McKinley has updated about these changes in her posts from San Francisco.
Cover Photos: From the minimum of 480 x 270 to 2120 x 1192 px size photos with a high resolution and aspect ratio gives a fresh and attractive look to your Google+ profile. They display in 16x9 when fully expanded.
Advantages:Option to use more imagesCreate collagesProvide more information in visualCreate an infographicAttract more customers with Business PhotosCreate GIF images to provide responsive engagement