According to the empyrion lore, the MS Titan was attacked by the Hyperion. Well, (PLOT TWIST!) what if the "aliens" rebuilt and refitted an upgraded version of the Hyperion, who poses as an fully automatic and hostile NPC endgame boss battle. It would require tons of building and resource gathering to defeat it, and it would make building massive ships worthwhile in SP. Furthermore different difficulties would be implemented in 4 stages:
Difficulty 1 - Hyperion CV with bad AI
Difficulty 2 -...
Idea for (Very) Endgame Boss
Difficulty 1 - Hyperion CV with bad AI
Difficulty 2 -...
Idea for (Very) Endgame Boss