So there are two major things in this chart. 1) previous market cycle retraced slightly more than 78% and started a new market cycle along the support trend line. 2) this new market cycle's 78% fib perfectly confluences with the great grand trendline (support). History suggests that BTC market cycle retraced 78% and found support at that trend line.
With that i think absolute bottom would be around that trend line and 78 fib.