I have no idea, have never heard that (and I stay on top of all WoW news every day), and an online search returns nothing. The only "nerfs" to rep since 4.0 is the guild talent Mr. Popularity
, which gives a 5/10% increase to rep gains at levels 3 and 11. There are the dungeon rep tabards, but those are only available for the major home city factions, along with those found in Wrath and BC.
Just hit 50 exalted two days ago, in fact, the tipper was my own guild faction.