When I first saw it, this sounded like the worst idea ever. Not only do I have to do the same crappy places over and over, but I need a specific tabard just to get the rep that I'd be getting anyway? This isn't a fun new mechanic, it's a pain in the ass.
Then I read it over again and looked at how other people interpreted it. After that I realized: this is a fucking great idea.
With this, I an pick which rep I get, no matter where I go. It doesn't work in BC instances, but I don't know the WotLK ones, so let's just pretend. SV isn't dropping my judgement helm, but I really need SSO rep. Just throw on the SSO tabard and boom, I can run SV for my hat and still get SSO rep. I trade a bag slot for... freedom.
This makes rep grinds a lot less irritating. It also makes a bit of sense when you consider that all our friends tend to be friends with each other, or at least share enemies. Thrallmar wants to see the Naga and Blood Elves defeated, even if the Fel Orcs are their main concern. The Cenarion Expedition would clearly be glad to see me deal with the Blood Elves or the Fel Orcs, in addition to their primary focus: the Naga.
This looks like yet another thing that Blizzard is getting right.