“With that in mind, we want to make it clear that TurboHUD4, like any game-modifying software, is prohibited for use with Diablo IV. Players who install this kind of software will put their accounts at risk for disciplinary action, which can include permanent suspension.”
I had never heard of TurboHUD4 before, but looks like it includes a map hack - which I can see why Blizzard is against it.
As long as it’s not on the ladder (have they released a ladder yet?) Who cares?
Because why open the door to any cheating in an online game? One with pvp as well.
Overlay type of mods are always kind of critical because they simply work in a very similar way to map hacks and bots, using often the same type of functions. Even if it wouldn’t offer anything offensive it would still likely be something their anticheat systems catch as a positive.