What makes Desktop Minecraft so fun is the creativity of the community,
and a large portion of that is on the part of the server creators.
In Minecraft Realms for Minecraft: Pocket Edition, there is no opportunity
for the server creator to add plugins on the server side.
Server software already exists for Minecraft: Pocket Edition that supports plugins, entitled PocketMine-MP. The software to write the plugins is already there, and the potential to connect to those servers is already in MCPE.
There are apps for Android that enable you to connect to these servers (PocketTool, BlockLauncher), and even proxies designed to do that without modifying MCPE.
There is therefore a community of these servers on the forums (MCPE: Servers).
There are lots of MCPE servers with Plugins, modifying the gameplay or disallow cheating, or even adding support for multiple worlds in one server. This shows how, Minecraft: Pocket Edition, can greatly benefit from plugin support, and the innovations of server owners.
The biggest limitation for these servers now is that MCPE currently does not support connecting to these external servers. This means that many players do not even know that this opportunity exists, and many cannot connect to these servers because they do not want to jailbreak their device or lack the technical skills to modify MCPE.
This is why an ability to connect to external servers via IP in the next MCPE update after 0.7.0 is needed. It opens up whole worlds of new possibilities for both the player and the server makers, and would be a huge leap forward for Minecraft: Pocket Edition.