If you want to be among The richest people on earth before 2020 then buy bitcoins now and hold. The way price is pumping up this days I think very soon maybe some where before the end of 2017 bitcoin might be trading above $2000. May the gods of bitcoin be among us.
2020 seems too early for your speculation, I agree with all your speculation except the timeframe. The gradual increase in bitcoin demand makes bitcoin prices keep on increasing every day. Hence it might need another five years at least to have some significant price levels like in millions.
Back to the topic, the best investment in 2017 must be bitcoins and I am very much sure in coming years too bitcoin will be achieving this. Because new investors will keep on increasing when seeing higher prices for bitcoin so this performance will continue.
I'm not sure that investors will be too active to join bitcoin. Now the price of one coin is too high and not everyone can afford to buy it.