DoF is actually easy to mod and it`s even possible to create new factions (if you now LUA, really good with 3D Max and photoshop and have plenty of time
However - the game files are protected, as otherwise there would be easy to create various cheats for Online Kingdom, and besides any changes to the game files will make Online Kingdom PvP/Co-Op go OOS.
The only solution is a Mount and Blade type of approach where player can decide to load up a complete Mod of the game with unprotected game files, and if there was enough interest our programmers could work on this, but this is quite a large project - and for now our priority is with new content.
If you have strong LUA scripting knowledge (required for DoF modding), have plenty of free time, and also work with 3D Max you can always try and enjoy our studio - in some sort of volunteer modder capacity, that was we`ll be able to set you up with unprotected game files and provide some in-house documentation. If you are interested just send me a PM.