From GTC 2016 Otoy’s conference. Starts at 5:33
So yea, apparently Octane render will be able to bake a scene directly in the ue4 viewport. The main advantage of path tracing and progressive rendering is that within a couple seconds you get a very good idea of how your lighting and shadows are going to look when the rendering is fully done. After that it’s just keeps refining. Right now we have no way to know because building a scene on preview is absolutely not representative of how a final production build will look like. We have to guess and I hate that.
Found this for Unity. The concept need to be applied to ue4!
This is basically something like this and god I would love that in ue4. You can see your lightmaps refining in real time.