I think it is very unlikely that bitcoin is replaced by ethereum and ripple. because I think the increase and decrease in the price of ethereum and ripple refer to bitcoin. I have observed in different exchanges if bitcoin goes down, another coin like ethereum etc will go down too. and if bitcoin rises ethereum will also rise.
I agree with your opinion. very difficult (and almost impossible) bitcoin is replaced by the ripple. Ethereum could replace Bitcoin. But takes a very long time.