They left out an important point (unless I missed it) - G.Fast only delivers those speeds over a short distance - 300m or so. Thus it is deployed close to homes and needs broadband transport, e,g, fiber or satellite, to get to the CO.
Out here in the West AT&T has deployed “FTTN”(UVerse VDSL) in most older neighborhoods...copper from the home to the neighborhood splice box then interfaced to VDSL/fiber then on to the CO. G.fast would be good in that situation.
https://en.wikipedia.org/wiki/G.fast
https://en.wikipedia.org/wiki/AT%26T_U-verse