The Blender Foundation is currently working on two different branches of their popular 3D suite, Blender 2.79 and Blender 2.8. We have discussed the former quite a bit, which is expected to code freeze within the next month or so, but the latter has been making noteworthy progress all along, too. It is focused on workflow changes, which includes updating the viewport renderer, both for preview as well as fast rendering of scenes that don’t require full ray-traced quality.
In this case, Blender Developers has released a video showing off how Cycles and Viewport can be combined. While you can preview what Cycles will output in the viewport already, enabling that rendered shading mode disables UI elements, like the movement widget. They are now being combined, and the Blender Foundation is aiming to make it fast enough for practical use.
Preview builds of Blender 2.8 are available now, and the Blender Foundation wants users to play around with them. Be careful using it for critical projects, though, because save files might not be 100% compatible, forward or backward, above and beyond the obvious stability concerns.