And indeed, just an hour after Rygarius posted this, the vendors returned! Blizzard are redefining "Blizzard Soon".
The issue was that, for some reason probably related to the conquest catch-up cap implemented last season, certain players had the full catch-up cap of 28,000 conquest points, instead of the correct cap of 2200. It's hard to be sure exactly what caused some players to have it while some didn't, but from the above those who abused the bug, intentionally or otherwise, are being relieved of their ill-gotten gains. A level playing field will be restored, and hopefully our conquest vendors will return to Pandaria before the reset takes place.