Improvements in existing features
Circles – Circles are probable the most important and praised feature of Google Plus. However, many users have demanded for more control over circles like merging them, arranging them according to their needs and roles etc. In the coming updates, Circles will get more features to allow users to customize them – rearranging, merging etc. Also the current limit of 5000 people allowed in to add to circles will be lifted.
Sharing – Again, this is a part of Circles. In upcoming updates, users will get more control over how they share. Users will be able to edit sharing settings of a post and add ore remove circles from the sharing. For example, if you shared a post with your friends and co-workers and then later decide to share it only with friends, you will be able to edit its sharing setting and do that.
Secondly, users will be able to share a post with anyone (publicly or with all circles) except selected people or circles. This is a one of the most demanded feature and it will be coming to you in next few days.
Another update will be the improvement to personal messaging. Currently you do this by sharing a post with only a person but if you forget to disable re-share or the receiver mentions someone else then your personal message can be exposed to others. In the next update, Personal messaging will become better.
Lastly, this is not sure yet but most probably hashtags (or somewhat similar feature) will be introduced to help tag the posts and make search better.
Stream – In next updates, you will be able to hide a selected circle to be shown up in your stream. This feature was also highly requested by users.
Secondly the menu will follow you down as you scroll down the stream, so you will not need to come back to top to open a different page. Another update will give you ability to expand and collapse comments. There was one more similar feature demanded by users that is nested comments. In the coming updates, there will be one level of nested commenting possible.