I don’t think it’s so easy for another coin to simply pop up and get adopted any more than another soda can come up and replace coke. Or another is to pop up and takeover windows, iOS, or Linux. It takes a lot of money to penetrate into the public psyche. Anyone in blockchain or crypto knows bitcoin. Bitcoin still controls the majority of crypto and when bitcoin up goes or down the rest of the market follows.
Bitcoin is software. It can easily adapt. It can evolve so if there is a vacuum bitcoin can change like it is doing. Will there be ups and downs? Sure. Will there be drama? Of course. Will there be room for other alt coins? Yeah but I bet the top 3 will easily take the vast majority , +90%. So I think bitcoin and if bitcoin then litecoin, and maybe ethereum. But hopefully Vitalik sticks to programming and no politics or phililosopjical crap.
And I do not count ripple as blockchain.
Just my humble opinion.