I found the artist who made the Rome 2 and Attila artwork, and it seems every picture had something to do with the DLC's.
The Rome 2 load screens like the German with dried blood is titled Vercingoterix, and then there is the Romans marching with Ceaser. Those 2 screens obviusly foresaw the CiG dlc, then there is the blood and gore dlc and the Dacia free-lc. It too had a Rome 2 load screen of a Roman being speared in the face by some Dacians. Or the load screen of Teuta of Illyria, which ended up happening with the Pirates and Raiders dlc.
Well the Artist has this image
Spoiler Alert, click show to read:
I heard some people think he was Belisarius, but the artist listed the piece as Justinian the great for Total War Attila. So i think there is a huge chance that this will be the first dlc campaign