A recent app teardown by Google Play Movies suggests that the app might be getting Dolby Vision support. The presence of the code doesn't necessarily mean that it'll become an actual feature. But it does hint at the possibility of the feature coming to the app. It also makes sense for the streaming app to get support for Dolby Vision. Play Movies already supports 4K HDR and HDR10.
Dolby Vision will improve on what HDR10 can offer, making it possible for brightness, darkness, and colour profiles to change from scene to scene. The code XDA Developers found hints at the app being able to inform you if the video you're watching supports Dolby Vision. Again, it isn't clear if Google will roll this feature out officially. But we will keep our eye out for it.