Wireless Network Design: The Troika
More cells, more antennas, more spectrum are the three major tools for adding capacity. To begin:
Adding antennas is usually the cheapest choice in 2018. Nearly every telco is going to four (4x4 MIMO.) Adding spectrum is very attractive when you have some unused but expensive if you have to buy it. Adding cells was the approach before LTE-A in 2014 permitted aggregation. Since then, tower building has almost stopped in the developed world. Any upgrade should include 256 QAM, more bits per Hz.
In a shrinking market, growth requires finding new customers. Adtran has been remarkably successful, beginning with a splash in Europe at DT. They've built a surprisingly strong presence in U.S. cable, mostly unannounced. Now, they've cut a deal with CCS to offer microwave backhaul for wireless to the rooftop, a promising market.
Jun Zhang, deputy chief engineer of China Telecom Shanghai, was surprised when this New York reporter called him and his colleagues heroes. They have connected directly to fiber more than 272M homes, twice as much as the entire rest of the world. 
Huawei has delivered a testable 50G unit to China Mobile and passed testing at the European Advanced Networking Test Center.
Softbank was startled by large signups for fixed wireless in Tokyo, a city with almost 100% coverage of fiber home. T-Mobile in Austria has also seen a trend.
AT&T is fibering 3M homes/year. Telefonica doing millions in Brazil and most of Spain. France Telecom is well along and nearly all of Portugal covered. Bell Canada recently decided to speed up fiber because cable was killing them. 
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.