It's great that it's being extended to the 18th, but I fully concur that some sort of accelerated leveling system would be a very 'nice-to-have' as long as players had the option to disable it. My wife just recently came back to the game after ~3 years away and absolutely loved the faster leveling. I'm afraid once it's gone she'll start looking for the door back to WoW again.
Personally I really liked the 12x class mission bonus from a couple of years ago, but the 250% was nice, especially combined with the level <> planet normalization that was introduced while I was away for a bit.
Really love the game, but as with all games I've ever played, level grinds are the epitome of "un-fun". Blizzard recognized this and listened to their customers. That game has practically no level grind at all, and it doesn't impact fun-factor at all, at least in my (and my wifes) opinion(s).
Your mileage/opinion may vary. Value mine what you paid for it.