Even the fastest CPU will never compare to a GPU. We're talking hours reduced to minutes for renders that are virtually equal quality. I don't think anyone who is rendering on a good GPU would ever go back to a CPU for any reason at this point. It's just not worth it, especially when the cost is nearly 3x what they paid for their PC with a high end GPU card.

The industry is going even deeper with GPU than ever before, so I think in the next 5 years, all rendering will be GPU based. Unless something crazy and unexpected comes up that changes the balance of speed, it's a no brainer. Even high end studios have started changing their render farms to GPU. Less time equals more profit.