When reading the title there is one word that is the most important when hypothesizing about the theme. In Warlords OF Draenor the most important word is of. This to me means one of two things, either the Warlords are from Draenor and the "of" is referring to their patronage or the "of" is referring to the Warlords ownership of Draenor currently. I think out of the two interpretations there seems to be much more "WAR" involved with the second, being the title is describing the current Warlords of Draenor. I think this expansion is going to be dealing with some very bad people running around remade outland plus all new zones added on.
p.s. Warlords from Draenor would be a less vague title.