I assume with such confidence, you have some sort of link or evidence to back up your claim?
Considering how slowly hardware is advancing now, don't be surprised if you are very wrong.
Hardware isn't advancing as slowly as you think. Remember, the XB1 is about 4 years behind a high end gaming PC; its GPU is a low end sku first launched in March 2012. But here are my four biggest bullet points for a 2018 refresh.
- DDR4, appearing already and mass production in 2015, solves the memory bandwidth bottleneck that plagues current APUs and IGPs. Look up some of the articles comparing DDR3 1066 vs 2133 on AMD's APU graphics performance. It makes a huge difference in performance, but its offset by the extra cost of the 2133 RAM.
- 20nm parts will appear in the first half of 2015. 16nm parts will appear in 2016. ARM parts alone will see pair of performance jumps for each of these. At the current TSMC 28nm node, you could create an ARM SoC that rivaled XB1 performance if you used active cooling and took the battery out of the equation. With a 2018 refresh time, the 16nm will very mature and 16nm parts readily available for both ARM and x86. You'll see tablets with performance that exceeds the XB1 before 2018.
- Console life cycles are usually ~5 years. The 7th gen was an exception due to the massive funds dumped into their development and the Great Recession. If they'd followed the usual 5yr cycle, we'd have seen 8th gen in 2010 and be gearing up for 9th gen next fall. Both MS and Sony seem to have learned from their expensive lessons with 7th gen and neither created unique proprietary silicon for their 8th gen. If one assumes they maintain this philosophy, which would be smart, a 9th gen on a 5yr tick would allow them to maintain profitability per unit sold while offering a significant bump in performance.
- Console devs right out of the gate needed to make concessions and reductions with their games in order to get them to run on the 8th gen hardware. Thats why we've seen so many high profile titles get their resolutions dropped to well below 1080, often 900p with a few 720p, and few hitting 60fps at all. Now we have to contend with PR/Marketing BS that claims 30fps is more cinematic. Mark my words, with the 9th gen arrives, the PR machine will hype up 1080p60. Ironically, while PC 4K displays are common place.
I know this is a DAI thread, but all of this has been rehashed before in threads in here, in Console gaming, in Gen Hardware, and CPU/Video cards. The current 8th gen consoles are simply too under powered to last a decade; MS and Sony know full well they won't and ceased the '10 year life cycle' PR months ago.