...The 4K and 8K development timelines appear close enough that IMO there's a significant chance for 4K to be skipped by the broadcasters and media companies...
The one difference is that 4K, with some reasonable advances in compression technology, can fit into a single OTA broadcast channel. 8K OTA would require at least 2 broadcast channels' bandwidth, even with significant advances in compression. 8K will also require a new storage and distribution medium beyond the current capacity of Blu-Ray, or again, really significant compression advances.
While a lot of people will go out and buy new TVs just because the technology is there, most people replace TVs only when the old one breaks. Since MANY of the HDTVs in use today are no more than 5 years old (not to mention the ones that will be replaced in the next 2 or 3 years), and figuring a 10 to 15 year lifespan for HDTVs, I doubt you'll see much of an installed base for 4K or 8K content before 2020 or so.
I don't doubt for a minute that UDHTV is coming, but I think it will mostly be delivered non-linearly (i.e. not broadcast), and won't be really well established until well into the next decade.