The PE/buyout and high yield boom in the 80s, the Asset Backed Securities and Prop-Trading boom pre-2008, and more recently the rise of Quantitative strategies - these are some examples of fast growing asset classes or practices within the finance industry that made some people very wealthy.
As the finance industry has matured, it has become harder to exploit opporuntities in slow growing sub-sectors. For example, starting a L/S hedge fund now is extremely difficult in the crowded space.
So what do you predict it will be in the near future - impact investing? a second PE boom? ETFs? Some niche thing that I don't know about? And why?