At the Minecraft Pocket Edition panel at MineCon 2012, as well as one of Jbernhardsson's livestreams, it was stated that future plans include trying to have a proper use for cameras, perhaps an easier way to take screenshots and share them with others. Since the addition of toggling the GUI on and off, the camera has becone useless except for taking a frontal picture. It's possible that they may never implement the camera because of this feature.
Johan mentioned on the issue tracker that the Nether Reactor may be replaced in the future. However, if the Nether does get implemented, it will most likely be next year because of preparations for the Beta Release.
Amir said to a reply that he plans to add a option available to add the current Realm your in onto your worlds menu, making it playable. It is on their features list and is planned to be added in Beta.