I agree that the interesting stuff here isn't the content of the announcement, but rather the format of the announcement itself. In addition to the bury-it-in-the-holiday-weekend timing, it puts a rather large spotlight on Josh D'Amaro not just as the DLR president, but on a more personal level.
I only view a limited number of Parks Blog posts, but I can't think of another one that features an Instagram post, especially so prominently. And it's not a post from one of Disney's corporate marketing accounts, but instead from the "personal" (but obviously cleared by corporate) account of DLR's local head who was allowed to release the information hours before the official announcement.
For people who follow these sorts of things, it's obvious that Josh D'Amaro has been a rising star in Disney's ranks for a few years, but he's still a very long way from being high profile enough to be any sort of household name. Looking at his Instagram feed, the oldest post is only from November 2018, making me think that this is part of a very deliberate strategy of some sort. The posts are all highly curated to present a rather specific public image, but it's still a mystery what that image is being so carefully developed for. He doesn't have the level of experience needed to take over Iger's job in a few years, but he's being presented in too forward of a manner to continue to be shuffled around as an upper-middle manager.
The announcement is just acknowledging one of Disney's worst-kept secrets. But the way that it was announced is what's really peculiar and newsworthy.