I have no control over when it is published -- Eden won't set a date "until it's ready", and that, in turn, is going to depend on playtesting, feedback, and so on. I certainly hope it moves along quickly, but I am just a writer, NOT an Eden employee, so I have neither control not information on the publishing schedule. We want to make sure the system works, and is scaleable, and is fun.
I don't want to go into extensive detail on the mass combat sytem, but I can say that it's designed to handle *large* battles (this isn't a 'skirmish wargame'), allows high-level individuals to have an impact on battles in a meaningful way, and incorporates all the rules you'd expect for magic and monsters. The book also includes rules for fortifications and sieges, and all of this is wrapped into a system for Realm management, allowing players to rule kingdoms, build armies, and send them at each other.
The actual combat mechanics are based on the basic principles of D20 (Armor class, BAB, saving throws), though they're slightly different in application. The learning curve should be very short, and full rules and examples are provided for building units from almost any creature type. Human pikemen? Hobgoblins mounted on pegasi? Ancient Red Dragons? All can end up on the battlefield. (And the dragon is very nasty....)