Roaming Boss Ship + More interactive events

So I was thinking of something that could spice up late game, a scary capital ship boss.

A quest will activate telling you rumors of a legendary ship that has annihilated countless star systems and your communication array just picked up a very omnious signal coming from *insert random system*. 

If you were to defeat it, you could salvage its incredibly advanced weapon and armor systems to be integrated into your army.

The capital ship itself would be enourmous and very powerful, so it feels like a legit challenge to take down. It would roam around the galaxy, laying waste to anything in sight if not tackled with a good balanced fleet, it will even do heavy siege damage to systems.

Design wise it would have to look omnious and out of this dimension, like the Riftborn.

Edit:

Adding to this, Endless Space 2 while already providing a substantial amount of events, it mostly revolves around flavour text events, it lacks in events that get you moving to places. The roaming boss ships is just the tip of the iceberg of what could be added.

Asteroid ; A faraway asteroid is inbound towards one of your systems, prioritizing heavily populated systems.

 If it hits said system you'll lose 80% and lose about 50% of impovements of your population, but gain a 30% increase in science across all other systems, learning from the impact and devastation.

If you destroy it in time, that system happiness will be set to estatic and gain a good amount of dust found in the asteroid

The asteroid must be intercepted by a fleet and be destroyed in "combat". It will create it's own unique node so your fleet can orbit it and erradicate it. It should take about 10-15 turns to reach said system, giving you enough time to reach it. One good fleet should be able to deal with it in one fight.

Dust levainthans; Space creatures mutated by dust. Using the animation of Horatios ships as a template, the addition of some scary creatures would be another good addition to add mid game. They tend to stay in special nodes. Killing them provides you with legendary armor for ships.

Minor Civ ascension; A minor civ under a new rule decides it's their time to conquer the stars, they start amassing a fleet and invade systems around them.