Excellent news. Discord is top notch at what it does, so better integration with Playstation's UI is very welcome. Microsoft needs to more deeply integrate Discord into their experience also because I want some of those features on Xbox, such as the nicknames feature for one. Let's see how Sony and Discord do this.
Seems people are misreading this? Even if Microsoft bought Discord it was never going to become exclusive to Xbox or anything, meaning partnerships like this with Sony would have still been possible, because they would have been an independent entity, and spreading something like this across as many eco-systems as possible is exactly what you want to have happen.