Anything that is not able to absolutely decimate path of exile in the pc-arpg genre would've been doomed to fail. As long as PoE is alive and kicking, there won't be a D4, or honestly, even a D3Exp2.
Blizzard knew this, so they went a completely different direction with mobile.
The problem is, mobile as it is is more tailored towards the asia market. It most certainly will be successful there. But having this in mind, announcing it with such a big ceremony was the big wrong decision here.
If they would've announced nothing (and just did this in some asia only thing....) or as a side note (like: oh btw we're bringing diablo to mobile, tailored for asia market, but you can play it outside of asia as well) it would've been better than this. everything would've been better than this.
This is the worst PR they could've ever gotten out of that. I feel really sad for blizzard, but the shitstorm which is brewing or already ongoing is self made, and thus deserved. But I still feel sad for them, because blizzard usually had great success with whatever they did. Or at least they hat like neutral reactions (HoTS being the only real thing which isn't a huge success I guess), and now they're getting such an overwhelmingly bad reaction from basically everywhere...