There is often a gap between availability of the technology and its commercial readiness.
Commercializing a product depends on market conditions. The technology can be available 30 years ago, but its commercialization is often based on consumer demands, industry standardization and the determination of the CE makers to make a go for it. But it is clear that because the CE makers already have the technology, then it is a matter of designing their products with PLANNED OBSOLESCENCE.
And the gap between technology availability and commercialization is getting shorter and shorter, especially with television. You only need to count the years between VHS to DVD, DVD to 2k, and now 2k to 4k. 4k and 8k technologies are available during the last decade. And CE makers planned their products accordingly.
Then there is the pricing issue. It will always be that the "new" products in the market have a steep price because the CE makers will want to recoup their investments and R&D efforts done years ago at least for the first year of commercializing the new technology. I remember DVD players costing $1,000 when it was first introduced sometime in 1997. It took Betamax/VHS to become mass-affordable in 8 years, DVD in 4 years, and BD in 3 years. Same with television. First generation HDTV became mass-affordable in 6 years, the new LED TVs in 3 years and 3DHDTV in 2-3 years. That is because these products have achieved market traction from existing customers who upgraded. In addition, the LED and 3D were merely enhancements of an existing technology.
Now if the 4k and 8k products gain the same market traction, I would guess they will become mass-affordable in 2 years. The faster the CE's recover their investment, the sooner the mass-affordability gets. It helps when the technology is not really new, but merely evolutionary so that the R&D cost is small. From 480p to 2k is considered revolutionary because it jumped from CRT to flat panels. But 2k to 4k to 8k is not. They only increased the resolutions using the same but enhanced technology. OLED is another matter.
Having said that, 4k units even if they become mass-affordable, will have to maintain a pricing gap from 2k products in the same class and release year, even if the manufacturing cost of 2k and 4k products are almost the same. Otherwise, no one will be buying 2k TVs anymore, unless they plan to kill the 2Ks.