Blizzard are like politics. They promise everything, even stars from the sky, but only before winning elections. Then they usually forget about such a promises. I guess, it's one of those populist statements, that give hope to some players and even sound like "promises" for others, so they continue playing, while waiting for it to happen in nearest future. But it's nothing, but empty words now. As you may know, we can't believe official announces now, not even just waffle during their interviews.
Without heirlooms leveling is completely ok now - no location outleveleving happens. But heirlooms are godsend. I have only about 40 days to play this game till I won't quit it forever most likely. And I need to bring 7 characters to at least 90lvl. 10 levels per hour won't be possible without heirlooms.