PCGamesN reports that Endless Space 2 got a new questline:

Endless Space 2's new hero is trapped inside a neutron star

[...]

As you might infer from its title, the Stellar Prisoner’s new questline concerns a mysterious figure who is literally imprisoned in a neutron star. It also appears that neutron stars will be objectives in a battle arena mode, conferring special bonuses to whomever controls them.

Features include:

• Neutron Star: a battle arena that provides bonuses to players who control this special node.
• A new quest triggered upon the discovery of the Neutron Star.
• A new Endless Virtual hero.
• A new Cravers Prime hero, unlocked by the community during an ARG.
• Two new, unique planets.
• Modding improvements, including the ability to edit visuals (hero, quests, events) and textures (planets, ships).
• General performance and AI improvements - there's a full set of patch notes here on Steam.

Thanks Farflame!