The Apple integrations will support AirPlay features you've seen on Apple TV and various smart speakers including multiroom audio, screen mirroring and streaming music from users' iTunes library. At this point Vizio hasn't announced an iTunes app like Samsung that will work on its own to pull in TV shows and movies. Support for HomeKit allows for smart home control of the TV from your various Apple devices, and lets it respond to commands made via Siri.
Not all of the enhancements are for Apple products either, as SmartCast 3.0 strengthens its ties with Google Assistant and Amazon Alexa. Google Assistant can launch apps, control playback, and in a demo we saw, even brought playback controls to a Google Home Hub. Control via Alexa is included, and the ability to launch apps with Amazon's smart assistant is due to arrive later in the year.