I would like to have your optimism... I mean, 10 years ago I heard exactly the same story: GPUs are not yet all-powerful, but soon they will be and will allow you to render stuff you never even thought possible... just one or two generations... just one or two problems to fix :D
That's all very true. I'm old enough to remember a company called Intergraph, who were trying to take on SGI at the time with Windows NT machines, boasting about their realtime rendering graphics system. They were showing impressive things at the time, which of course would look hopelessly simple by today's standards.
Still, if different product strategies are viable but on different development trajectories, and one is potentially a better long term solution, their performance curves will eventually cross and after that point it is no longer one or two generations away, it has happened. And I agree with Philippe, it is not so much about the final render as it is about the interactivity getting there.
I'm not familiar with Redshift, but if a serious player comes out that is similar to Corona, but focused on GPU instead of CPU, it could become a very successful product. I really love Corona and their desire to remove all clutter from the renderer, realizing that not everyone likes to tinker with render settings. (Having come to the point I'm at today together with and because of Vray, I actually feel disloyal to Vray saying that, as it clearly is a comment directed in that direction, but I just can't do it anymore. Vlado and his user base is either just to smart for me, or they are too interested in render technology in itself. Quick Settings aside I've long ago given up that they will clean up and automate the interface and every suggestion to make it more elegant, like a material preview shader, is apparently a waste of time that no one will use anyway.)
Philippe, I actually find Max both fast and capable, what would be the alternative? If one comes along I'm sure creative forces like Juraj, Guthrie, Bekenman, Bernard and the other usual suspects will jump ship and we'll all follow along, just like we did with Corona. :D