Let's play a guessing game: what sort of mods will we see for Total War: Attila [official site] now its official mod tools are out? Game of Thrones, that seems an obvious world to bosh into a medieval strategy game. Probably Warhammer Fantasy, I'd imagine, even though Total War: Total Warhammer - War Tote is now official. All sorts of rebalancing and tweaking and prettifying and historical doodads too, I'm sure.
Total War devs The Creative Assembly released Attila's Assembly Kit yesterday, which can make all sorts of mods and comes with Steam Workshop support.
If you have Twatilla (a nickname I came by innocently, I assure you), you can find the beta tools in the Tools section of your Steam Library. They're mostly the same as previous Total War mod kits, with tools named after men (DaVE, BOB, Ted, and Terry) that let folks change the game's database, textures, animations, models, battlefields, and campaign map.
TCA do note, though, that "Unlike previous Assembly Kits, Terry now grants access to Terrain Raw Data, which means modders can determine which battle maps load in for specific campaign map locations. Go mod those cities!"
If you fancy making your own mods, the Total War wiki has brief introductions to how all the tools work. If you want to see moving pictures, here, a brief overview of the tookit: