Not true. DirectX 12 will be the standard within a few years, and while quad-SLI titans is a ridiculous requirement, that type of graphical fidelity is technically achievable right now. Which means that within 5-6 years, the price of the tech needed to reproduce such high-end graphics will have dropped dramatically for gaming PCs. I do agree with the diminishing returns thing, however, and a 'realistic' aesthetic has never been my favorite.
Truth be told, this tech demo doesn't even look that much better than games like Far Cry 4 or Shadow of Mordor when you max them out. Speaks again to the diminishing returns. You can only add so many polys to textures before people can't notice the difference any more.