Comcast just updated their Xfinity app (2/28) to the new Xfinity stream app. At work so cant easily check to see if it side loads and works or not but figured I'd pass it along to see if anyone has tried yet. I know the old app wouldn't work past a certain version and if you were running Android 7 none of them would work.
Not sure about sideloading, but I can confirm the screencasting detection is still in effect if you try to cast from an Android phone.
They have the nerve to make the headline description for the app read "Only XFINITY gives you more to stream to any screen ."
Fucking liars. They also disallow their login credentials for every TV app that I'm aware of on Android TV.