Its likely it wasn't pulled at the 11th hour, but that this announcement was pulled from Blizzcon weeks ago is pretty clear at this point. If other 'people' are to be believed, I forgot who posted the link, but apparently they also pulled D4's announcement prior to last year's Blizzcon as well, which is just more fuel for the development turmoil narrative.
My message to Blizzard - at this point, just announce the stupid game already. Its not like you guys have ever had issues with cancelling games that either had gone through too many development processes with nothing coming about or the games never reached your quality standard. Warcraft Adventures, SC Ghost, & the pre-Overwatch Titan all immediately come to mind.
Blizzard is openly responding to rumors to Kotaku about a game they never officially announced, for what reason exactly? This is such a silly situation Blizzard is placing themselves in by not announcing a thing they are still talking about anyway. One of the biggest rules in PR is to never let the story get away from you and in the span of a weekend, Blizzard has gone from seemingly this super secretive dev house to having one of their most active dev teams stuck in a development hell of sorts, with a PR team that is so out of touch with the fanbase they never imagined there'd be a backlash to announcing Diablo Immortal the way they did.
Blizzard, stop using the 'we have multiple Diablo projects in the works' as a shield as well to not announce a game everyone already knows about, in which you're already responding to rumors for. You're embarrassing yourselves.