This total overhaul of Rome:Total War is based upon the Second World War. It contains historical battle locations on different fronts.
Bulgaria has Panzer IV units now. They have also gotten their roster-picture updated just now. Dagovax/Sirrianus is not finished with any of the smalelr factions and will most likely add artillery/tanks/planes to some of them if not all - at least they will most likely get artillery and tanks - while planes might not be for everyone. But those that had planes historically are likely to get just that.
The problem is the limit of just about 90 mounts in both Rome and Medieval 2, which has already been reached (horses, motorcycles, jeeps, tanks and planes are mounts) and also the 200 unit limit is also pretty much reached with only very limited unit slots left for the Neutrals and the planed Dutch East Indies faction - forcing Dagovax to use the same skin for some tanks.