You mean it wouldn't be fair to people who already have it that don't want anyone else to have it? I've said it elsewhere before, but that's an Ivan the Terrible mentality.
I've bought stuff that came with pre-purchase bonuses before, I don't care if devs charge extra for it after the game releases as I got it for free.
It can't be called a "pre-order bonus" if it's available later on.
Again, it is a bonus if you pre-ordered the game as you got it for
FREE, it wouldn't be a bonus for people buying after the release as they have to pay for it. Arguing the semantics doesn't negate what I've said.