I don't think Revelations 2 swapped enemies around like Rev1 did, it just had extra enemies on top of the exact same ones on lower difficulties.
Putting a difficulty behind a pre-order bonus is stupid though. The first time through a game is always the best for horror titles, if you need unlock it and replay through then you get a diminished experience since you already know the layout of things, how to deal with things etc etc.
That's what I meant for Revelations 2, not to imply differently, but they added some additional enemy placement on Hard difficulty to make scenes trickier. Revelations 1 HD had Infernal Mode, which was completely remixed to the main game, but Revelations 2's hard difficulty added a few extra enemies to make combat/stealth both harder in certain segments, basically strategically placed additional enemies to provide more of a challenge on hard.
I agree with you that locking it behind a pre-order to be available from the start is dumb, and I think if it works better as an unlockable to be an unlockable or just available from the start for everybody if it doesn't work best as an unlockable. It's my whole dilemma over this as someone who will be pre-ordering anyways though, for any horror game, even if its procedural generated or whatever, the first playthrough of a horror game is crucial. You will never have that first blind run ever again. Good horror games can of course be a lot of fun to replay, but enjoying them the first time through is crucial and a different sort of thing entirely. So that's why I'm sort of split on this, and I hope they do release some more information on this.
If the Hardest difficulty is just the base game, but... Harder. Then I think I will want that to be my base difficulty to play through the first time since I enjoy my first blind run to be against challenging odds, its how I play almost all my horror games, on the hardest possible option from the start, but then if it's just that and it's locked away from the beginning for non-preorder consumers, that's dumb.
On the other-hand, if it's like a mode that expects you to have played the base game originally and then throws in some big curve-balls that messes with expectations and provides new challenges not in the regular difficulties, and designed to be played after the main game, then I don't really want that to be my first run of the game but a subsequent run, in which case why even have it unlocked from the start?
I am going to pre-order the game as I said, I think RE7 actually will be a really good game, and I am excited for it. But I think this particular difficulty pre-order decision was dumb from either angle, but I hope they at least clarify since I want to know which difficulty I should be playing for my first run as someone who usually plays on the hardest difficulty in horror games available from the start, but appreciates difficulties that 'remix' and change major things for a subsequent playthrough.