that 5k resolution
is 2000p, only with extra width. The single figure resolution is invariably for number of vertical lines. Also, for cinema maybe higher resoltuions will one day appear. But in almost all homes 1080p is the limit of size versus resolving power of the viewers. If there is another definition increase it'll likely only be one more resolution upgrade from 1080p. By the time you have a 40" 4000x2000 TV, you probably won't physically be able to see any difference between that and a 40" 1080p set, and certainly an 8000x4000 40" display will improve nothing over the lower resolution 2000p. I'd say we'll only get one more resolution before framerates become key, XD or Ultimate HD or whatever PR twist they give it, and then maybe some totally new tech that doesn't worry about being tied to a High Definition type name. Thus the HD name fiasco can be solved with HD > EHD > XD as probably the preferred choies (High def, Enhanced High def, Extreme Def).
It's also worth pointing out that when you say 'today' you mean in prototype form, and the actual rollout is suggested in the article at 5-10 years