What's the Next Hot Financial Sector/Product?

There is always a hot, desirable field in finance. Asset Management providing ETFs, or passive investing is hot right now. Mortgage backed securities were popular in the '00s before the recession. VCs and tech stocks were the thing in the '90s, before the dot-com bubble bursted. Junk bonds grew a lot and were especially lucrative in the '80s. Meanwhile, algorithm trading and hedge funds have also peaked before the recession and are past their prime.

Passive investing might be peaking, due to an arguably overvalued stock market. What is the next big thing? Is it emerging market equity, or real estate? Do cryptocurrencies have room to grow? Finally, Everyone loves private equity, but the market seems to be becoming saturated with PE funds. So how does the rise and fall phenomena of other sectors and products apply to PE?