Empty MMO maps, huh? The formula isn't different to classic DQ games, there are no excessively large areas, the next town or other big point (linearly for the most part) is always just a short trip through a monster infested area with few points off the beaten path for a treasure chest or whatever.
People who have the original don't care for the new content and changes as they aren't significant and people who didn't have it will buy the new version so, that's how they get a "free pass" with it I guess. A 50% discount for owners would have been nice, like paying 20 for the additions. Oh well.
I don't think it should be a patch though, the versions should be separate entries in the library regardless, you'd definitely have people complain they can't play what they bought on day one as it was and as they prefer this or that aspect of it any more, since it really isn't just a patch over it either.
I'd love if they included the 3DS version too, imo that and the 2D mode are far more fitting for a game of this sort instead of trying to make it like a cinema-tastic modern Final Fantasy or something, it's all way too traditional (the whole point of the DQ series) for that stuff to fit in well with it all.
But I suppose like the PS4 version it was never updated with the S additions either. It's all bad development from Square so it couldn't be merely patched up. They made the 3Ds 3D + 2D, with a separate PS4 version like a full remake, then they made the contract with Nintendo for the extra stuff on a Switch version and didn't actually make it for the PS4 version and then downgraded/timed it for the Switch but instead worked only on the Switch fork and now that's getting ported over to the rest rather than work to upgrade that stuff and insert it in the original PS4 base. It's a huge mess!