If the progression of other live service games is any indication the only difference between how those games operate their battle passes and how diablo 4 will operate is the time it takes to ingrain it into their community.

I doubt this initial battlepass will have anything too egregious to start but as the game progresses more and more they'll start to add in items and services that drift the battlepass into more predatory territory and if they do this slow enough or cultivate their whales hard enough they'll be able to continuously move their communities goalposts. I'd imagine they'd want to avoid going full diablo immortal right now as I think the general perception of that game to most people semi-familiar is that its a gacha mobile game with a diablo skin and they'd likely want to avoid that until they have a more dedicated player base to exploit.

tldr: This battlepass probably won't be too bad to start but overtime it'll get a lot worse.