Remind me, how many different factions of Rohan do we already have rep with?
Also, given how the Allegiance system is set up, adding Rohan (which falls under Man) makes little to no sense.
The devs don't have to create another Allegiance grind simply to tell a story about Rohan--they could simply just tell a story. With all the tedious grinds in this game already...
I think that is what most are getting at. That the sub-factions be included within these allegiance systems. The allegiance system was described as the new end game solo content, and I presume the black book will continue on in further updates. While we pledge our allegiance to men, I'd hope it is to all the factions of men, so that we are not only running around Minas Tirith in Gondor, but that it sends us forth to show loyalty and frailty to the other factions - like Rohan. Same for Dwarves, Elves and Hobbits.
Sometimes, no matter how hard you look, there is no best light.