If such a scenario is possible, it will clearly not happen this year. Maybe in a few years.
Honestly, I still don't get this assertion that coins are "joined".
They're "joined" in the sense that they're both cryptocurrencies and in the same market, but there is no other tangible connection between them. They're competitors.
Yeah, there's a lot of mystical mumbo jumbo about primary coins on exchanges and yada yada, but at the end of the day they're separate coins, just like Ethereum and Stellar are separate coins but vying for market share.
Ethereum is a more compelling solution in some ways than Bitcoin BTC, and BTC is broken and intentionally so. Ethereum is just progressing along as it should, with lots of hard work being done to speed it up via sharding etc because it genuinely has a high workload now, and it deserves to gain more market share.