I think a better alternative is to put 80% in TQQQ and 20% in GLD.
So the number looks like this:
If you hold all TQQQ from the inception,and there is no 90% drop, you make like 100 times.(the number may not be accurate.)
If you hold 80% TQQQ, 20% GLD from the inception,and there is no 90% drop, you make like 80 times.(the number may not be accurate.)
If you hold 80% TQQQ, 20% GLD from the inception and there is 90% drop in the first year, you inject GLD in the first year, you make like 110 times.(the number may not be accurate.)
Why I said this is a better alternative?
Because what if the 90% come in the second year or later?
In that case, TQQQ will first rise and then drop, so the number after its drop would be bigger, and GLD injection would play smaller role.So leave smaller capital in GLD would be better.