Your cable provider's set top box is the final frontier where the Apple TV app can reach. Variety reports that Comcast announced in its most recent earnings call that the Apple TV app would be available on Comcast's platforms within the "coming months." Viewers who have Xfinity X1 set tops, Flex streaming hubs or XClass TVs will be able to access Apple TV+, in app channels (like AMC+, Showtime, and Apple's usual video rentals and purchases.
Comcast will also bring its Xfinity Stream App to Apple TV hardware in exchange. This will allow you to use your Apple TV device as a stand-in or to view broadcasts on another TV while you're away.
This expansion may prove to be more important than it appears. Apple's streaming video app can be used on many smart TVs as well as dedicated media players and consoles. However, there are many people who think their cable box is the most intelligent device in their living room. Apple TV+ is now available to many who would not consider it if it required a new TV, or any other device than the ones they already have.