Blizzard put up a preview of a couple of Tier 9 sets over at the Under Development section of the official website, and they look pretty interesting. As previously suspected, the Tier 9 armor sets seem to share visual characteristics with the same armor class. In the examples that Blizzard shows, the Horde Shaman and Hunter -- both mail-wearers -- are similar in appearance. Two other examples are the Alliance Priest and Warlock, cloth-wearing classes, who look largely similar.
The good news with these faction-specific armor is that the design team has put a decent effort into making the sets somewhat distinguishable from one another. For example, the Horde Shaman's shoulders are reminiscent of the Earthfury Epaulets from Molten Core, distinct from the chitinous design of the Horde Hunter. The Alliance Priest and Warlock designs are a lot closer to each other, however. But don't take my word for it... head over to the Under Development page and check out the previews for yourself. I'm pretty stoked and can't wait to see the rest of the sets!