SoftBank says that massive MIMO is the key element of 5G. It is true on the view on radio propagation. But 5G has a lot of parts for its architecture. So it is difficult to say for us what is the key part of 5G.
Massive MIMO is one of the important thing. If we can not achieve the high performance of massive MIMO, we will lose the high throughput and high capacity. It means that the costs per bit will higher. All mobile network operator must cut the costs for network operation and provide the reasonable price, so they should achieve high performance with fewer base stations.
To integrate the Massive MIMO, the vendors try to development and evaluate it. But, is the mobile operator need to try it? Using massive MIMO, should the mobile operator change the technics how to deployment base stations and antennas. I don't know whether it is or not.
On the view that, Softbank say that massive MIMO is the key part. It is important things for mobile network operator to know whether does massive MIMO make mobile network operator's view on the area planning or not.