Nostalrius was a private World of Warcraft server that gave players the opportunity to play the game in its original Vanilla version. For this reason the server managed to become so popular that at one point it even had a bigger active player base than most official Blizzard servers. Seeing the popularity it gained, Blizzard sent out a cease and desist letter to Nostalrius, and the server went offline during April 2016.
Nostalrius players urged Blizzard to make their own Legacy server, 250,000 users even signed a petition in which they said that they are going to pay a monthly subscription to Blizzard to be able to play on a Legacy server. Blizzard took note of that and they said they are working on releasing a new Vanilla server, but they are encountering some unexpected problems since they deleted the original Vanilla source code.
WoW players were expecting Blizzard to officially announce when the new Vanilla server is going to be launched at BlizzCon, but instead Blizzard focused on the launch of the new Legion patch. For that reason Nostalrius has decided to give their Vanilla source code to another private server called Elysium.
Elysium is going to be the next big Vanilla server, and some of Nostalrius older developers are going to work alongside the Elysium crew in order to create the new server. Nostalrius themselves have said that they are going to personally help in the creation of the server, they are just going to give them the tools to do it themselves.
To pay respects towards Nostalrius, Elysium has announced they are going to import all characters that were created on Nostalrius to their own server, meaning that Nostalrius players do not have to start from zero again.
The main concern that players have is that Blizzard might take legal action against Elysium, the same way they did with Nostalrius. Maybe Elysium has figured out some loop holes.