Hi there,
Just wanted to let you know that Blizzard will 100% refund you for Legion pre-purchases (even if you have used the boosts - they will lock the same character until and/or if you pre-purchase again) by contacting support via live chat / web ticket / phone.
Although I will probably play it, I am very skeptical as to how the game is coming along at the moment so I'd rather see what happens before buying it.
Just an FYI so people have the option to make an informed choice.