Pocket Edition mentioned features
Many features have been mentioned for inclusion in the Pocket Edition.
Note that this page only documents features that were mentioned but are not yet in the game. Features in development versions are described on the parent version page.
Tomasso stated on reddit that he would like to add a "difficulty" number that mobs could have depending on their circumstances, such as resource that it spawns from and weather. This would vary the amount of hostile mobs at night and the amount of recources gained from each biome. He also stated that he would like more biome-specific mobs as well as biomes with specific difficulty/mob distributions.
Other world sizes
Tomasso stated on reddit that there may be other limited world sizes in addition to the current "Old" world type (256x256). These world sizes could be 1000x1000 and 10000x10000. When Realms is re-added, it may have a limit of 10000x10000. 
When it was mentioned at MineCon 2015, the response was that it should be in this year. When it was mentioned in the Pocket Edition Q&A Lifestream, it was stated that Shoghi was working on authentication and it should be coming soon.
From the PC version
The developers have mentioned many features from the PC version which will eventually be included in the Pocket Edition.
- Ender chests
- Bonus chests
- Item Frames
- Riding pigs
- New sound engine, jukeboxes and music discs
- Varied minecart types and more redstone-related blocks and items - should be this year
- 256-block height limit
- Hardcore mode
- Stained Glass
- Texture pack support
- Twitch streaming
- Survival interfaces in Creative
- Sharing worlds
- Server plugins
- Resource packs
- Ocean monuments
- Boss fights
- Book and quills - may be implemented through voice dictation
- Witches and witch huts
- Ability to use chests in creative mode
- Multiplayer authentication from Mojang servers
- Mojang account sync on Pocket Edition (i.e. being able to use Mojang account for skins etc)
- Enderpearls and the End
- Easter eggs from the PC version (e.g. renaming jeb_ or dinnerbone etc)
- Some way to display coordinates without an F3 menu
- A recipe book which contains all crafting recipes, should MATTIS be taken out in the Windows 10 version
- MCPE for Oculus Rift and maybe Google Cardboard
- The ability to remap long touch to hardness-based touch (3D Touch) for iPhone 6S
- Ability for really large contraptions to work in unloaded chunks
- Splash screen for Android devices
- Creative Inventory, like the PC version.
- New Buttons:
- Dye [Sheep]
- A version exclusive underworld underground structure
- Cave Culling 2.0
- Change of GUI button texture
- Multiplayer chat scrolling
- Demo/lite version re-release
- Programming interface
- Copy worlds
- Tommaso mentioned adding 3-D grass on grass blocks; although he decided against it as it was expensive and clashes with the style.
- Windows 10 Edition only structure - seen in demonstrations of the Windows 10 Edition at MineCon.
- The following mobs were mentioned in a Q&A session, which although far fetched were tossed around - penguins, llamas, alpackers and wizards (but not spell-casting)
- A dream dimension