[Skie]

Sky Q does it. You can scroll through channels and after a second the preview image turns into a live pip of that channel. One of very few things the Sky Q box does better than the V6.

But it really isn't hugely useful outside of being able to join a channel that isn't showing adverts. Actually being able to choose a channel to put in a bigger inset window, with audio going to a separate output like bluetooth, now that would be good. Many TV's can do it already, but they tend to not have the breadth of channels a cable/sky box might have so it does limit choice.