So here it is a week later and we are all still waiting for a proper, stable release of Pocketmine v1.0.
Elywing is the only build that has been releasing 1.0 compatible updates, but they are extremely buggy!
***2016-12-29 UPDATE: BlueLight is another 1.0 compatible build from a small group of Japanese developers that looks very promising.
EssentialsPE MUST BE UPGRADED if you want to use BlueLight, as the old version prevents players from connecting to your server.
Due to customer demand, we have also updated the MOD installer/upgrader script to allow switching between Pocketmine builds of the same major version while retaining existing worlds and plugins.
1: A "major version" is like: 0.15.0 or 1.0.0 or 0.14.8.
A "minor version" is the build #, like 0.14.8 build #247
2: Changing from a NEWER major version to an OLDER major version (downgrading) WILL NEVER WORK.
Because of this, the MOD installer/upgrade script will archive and then delete your world and plugins to prevent crashing.
This applies to all Minecraft versions and most games. Newer items, features, entities and mobs are added to new releases that the older software does not know about. Attempting to use older software with a world from a newer version WILL CRASH YOUR SERVER.
3. Switching from an OLDER major version to a NEWER major version (upgrading) will always retain your plugins and worlds.
4. IMPORTANT: A world generated in one Pocketmine build MAY NOT BE COMPATIBLE with a different Pocketmine build.
As for the other Pocketmine builds, they have mostly silent since the 1.0 update from Mojang/Microsoft. This is due to the date of the release (Dec. 19th, just before the major Christmas Holiday), and the complexity of the changes.
Here's what one of the official Pocketmine developers has to say on the subject:
Monday, December 26, 2016