12 bonded lines of 35b VDSL should be able to deliver 2 gig downstream ~400 meters. That's comparable to the most common G.fast backhaul, 2.4 gig GPON. Telcos are confident few will use the high speeds simultaneously so the high over-subscription is realistic. Upstream on the older DSLs is lower, so the upstream will probably be limited.
Kurt Raaflaub says Adtran has trial units at customers. As far as I know, this is the first public description of bonded 35b and I hadn't anticipated this possible use. Deutsche Telekom says 35b will be ready for deployment the second half of 2018.