BT has found success in the lab by upping the power, adding more bits/carrier, and modifying the Power Spectral Density. The standard is being revised and the chipmakers are working furiously. Blue and green lines in the chart project the results from a model by Daniel Hincapie and Mathias Leibiger of Fraunhofer, presented in an EE Times article. A map is not the territory and simulations are not working chips, of course.
Their simulation projects an improvement of 150-200 megabits at loops under 100 meters, typical in apartment buildings. Lucky tenants will get a gigabit, a crucial goal for AT&T. They will be selling G.fast as part of their Gigapower offering, so they needed the gig for marketing purposes.
At 300-350 meters, BT's target distance, the newer units may raise speeds 20-40 megabits. Above 400 meters, there is little difference expected.
Kevin Foster of BT strongly endorsed the changed standard, which is based on testing by his colleague Trevor Linney. Rami Verbin of Sckipio is confident he can deliver the chips. Everyone's hoping for early next year, but nothing's certain.
Caution. People lost their jobs - and Ameritech lost tens of millions - when early ADSL fell 20% short of simulations.