Given the recent trajectory Activision Blizzard has been on, I'm basically expecting pay to win at this point. I don't think it will be quite as bad as Diablo Immortal, but still pretty bad. Lootboxes are pretty much a guarantee, and I'd be amazed if they didn't at bare minimum include various potions and scrolls that are slightly better than what can be found in game. Wildly overpriced cosmetic items, for sure, many of which individually cost almost as much as a whole new game.
It's almost like they are chasing after EA. I'm beginning to wonder if we're going to see a Diablo 5 in a couple years, which is literally going to be Diablo 4 with a number "5" sticker on the cover. At this point I wouldn't even be surprised if you had to buy card packs to unlock the character classes.