You know that the most popular private servers out there are actually 1 x servers? And you can't conclude that it will increase the server population for sure. There are many factors to include.
Some people don't play on Lordaeron because of RDF being disabled for example. Or that the raids are buffed.
Why do every server need to have 12k population? 12k is A LOT. One year ago people would say 6-8k population was insane, but after the hype was on lordaeron a new standard was set.
If you don't like to level up at 1x rate, find an other server. I like it. I would be really angry and sad if they just changed the rates, because of people who don't really like how the server was set up to be.