> This $8T difference feels tantalizingly close to new investment money flowed in via ETFs

FT says it is about $2T net in the past 8 years, and about a third of volume today[0].

Also an interesting article because it talks about the potential issues on market volatility ETF inflows introduce

[0] https://www.ft.com/content/d12ac93c-a507-11e6-8b69-02899e8bd...