Galaxy Research projected ~14bn of ETF inflows year one.  We're sitting at 53 billion total AUM right now in ETF's.  Not sure this a completely proper analysis as it already factors in what was under management with GBTC but even so... Blackrock alone has taken in over 17 billion alone.

https://m.primal.net/LwmD.jpg 

https://m.primal.net/LwmF.png