Although you typically need to have a set-top box from Comcast to have access to their Xfinity TV service, Comcast has been working on developing their own standalone app with a subscription service that would allow customers to stream Xfinity TV content without the need for a Comcast box, similar to the way you can subscribe to and stream content from Hulu and HBO Now. Although the app is not yet available on a wide scale, it would appear that the app is already running on NVIDIA's SHIELD TV device as it was shown off at the INTX 2016 conference during a Comcast demonstration.
While this may not seem like such an exciting thing at first, for those who want access to Xfinity's cable services but aren't really wanting to lease the set-top box, it's a huge deal. This is made all the more interesting that there is already an Android TV app that works considering Samsung was the launch partner for Comcast when they announced the plan for this app, which should see the service available on Samsung's smart TVs. As of right now, the app is not actually available to the public, so if you were hoping to download and install it to your own NVIDIA SHIELD TV, you're out of luck for now.
It's entirely possible that Comcast may one day release the app for the NVIDIA SHIELD Android TV or other Android TV devices, but they may never launch the app, and NVIDIA isn't giving any details other than the fact they're working with Comcast on the application, and that the app was being demoed at INTX, stating that they "have nothing to share at this time." Even though there is nothing to currently install, it gives Android TV owners and specifically, those with the NVIDIA SHIELD, something to look forward to. If you're a Comcast customer already, then you're familiar with the monthly cost that gets tacked onto your bill just to have the set-top box sitting in your home. This app would do away with the need for one, and would save you a little extra money each month, which would certainly be a good thing.