Few people spot the next big trend as consistently as Masayoshi Son. Under his leadership, Japan’s SoftBank pivoted from an internet broadband provider into a mobile phone network company and most recently an investment giant boasting assets worth $180 billion. Today, Son is pivoting again into what he believes will be the key source of future growth: AI, which he’s backing with $9 billion a year in investments. In May, SoftBank led an investment of over $1 billion into British self-driving car start-up Wayve...