sounds a lot like Eve online set in medieval times. Guild Wars had a similar system where you could choose a faction and battle other factions to win reputation etc but was nowhere as dynamic as you're describing. also kind of sounds like Dynasty Warriors which kicked ass but followed a more traditional set path of battles
all of these are great games and a blend of them would be awesome if you had a clear vision for how to combine them, but would also probably be a massive undertaking
side note, i wouldn't consider anything a true RTS unless it has some type of resource gathering and tech/unit building element to it