The grand strategy epics Crusader Kings and Europa Universalis are about as famous for the insane mods people create as they are for the tales of regicide and arranged marriages.
The default models in Stellaris, however, aren't as naturally attuned for a Game of Thrones or Star Trek total conversion. But that's OK, because Paradox has a solution.
A week out from the launch of the 4X/grand strategy epic, Paradox has released the company's Clausewitz Maya Exporter. It's a tool that allows modders to create their own assets and avatars that can then be imported into Stellaris.
It's a pretty simple idea — if the game's base models and textures aren't suited for, say, your recreation of Battlestar Galactica, then simply make your own. You'll need to have access to Maya and Photoshop for the texture importer, although that's a barrier to entry that most modders have no difficulty surmounting.
The tool is partially compatible with Crusader Kings 2 and Europa Universalis 4 as well, and it fully supports Hearts of Iron 4. There's no tool for other asset-making software like Blender, although Paradox has pledged to publish their .mesh format "so that anyone willing and with the skills can write an exporter for other software".
With this out, it shouldn't be too long before people start reskinning Stellaris in the vein of Star Wars, Star Trek, Master of Orion, Babylon 5 and Farscape. Hell, there'll probably be a Highlander conversion before too long.