That said, I'm not convinced that path tracing and physically-based rendering methods will ever completely replace rasterization. For some applications (especially games), the kinds of non-realistic effects you want to achieve are actually very hard to model and render using techniques that aim for realism. Probably for games we will end up with hybrid rendering that uses both at the same time.
- What you said is true of any rendering method you use. If you have a complex scene, it'll take more time to render one frame.
- What I said about 2018 or 2019 is what nVidia's promotion is all about. See the demos linked at the bottom of my comment. They keep calling it 'real-time ray tracing' but it's really 'real-time path tracing'. And it's already happening.
[1] https://www.youtube.com/watch?v=Vdnwrt3Xdak
If you're trying to demonstrate the 'real world usefulness' of raytracing in games, the appearance of shiny ball bearings is a clear sign that you've run out of ideas.
[1] Looks really good but only one light source and barely even a bounce of light. Nice backlight halo, but that’s not ray-tracing.
[2] Obviously a lot going on here and some progress of some sort but if only all the reflections weren’t so blurry. What’s up with that?
[3] 99% of what makes this scene look good is the PBR texture tuning. This lighting does not look good and nothing is moving. Very few reflections and small but they do look proper.