The GameDVR is nothing new and has been a part of the Xbox App since Windows 10 was launched. You have various max recording length options ranging from 30 minutes to 2 hours, you don't have to let it go the full length and can stop recording whenever you want but if you hit the max you have to manually restart the recording. As far as I know the GameDVR doesn't currently have a built in streaming option though it looks like Microsoft is changing that with this update.
You would think if everything works correctly that both lower end and higher end rigs would get an improvement but that it will more noticeable on lower end rigs. Of course when do things ever work correctly?