If streaming is currently reckoned to be around 10% of UK viewing (can only dig up a figure of 3.8% for 2014 but with growth that seems about right) then getting to 100% (which of course it won't ever need to) doesn't seem that big a stretch given advances in codecs, telecoms kit and more local CDN servers (which the big video delivery services do pay the ISPs for).
Interestingly, according to Ofcom the biggest decline in traditional TV viewing in any platform was when Netflix launched on the TiVo and were offering the six month free deals. That and a ton of other interesting info on viewing habits here:
http://stakeholders.ofcom.org.uk/bin...ing_habits.pdf