Still works. Basically what you do is that you create premade outfits in the transmog tab when you're alliance and when you faction change, you can use those sets as they are on the alliance without them being converted to the horde version.
But you'd have to pay for a faction change for that.
You could buy the alliance pvp tabards as horde from the tabard vendor in Shattrath for like 2 weeks some time early Cataclysm. Still have the Silverwing tabard on an old alt from then.