Bitcoin will likely keep being number 1 for at least another year, yet it will be surpassed by other new cryptocurrencies with better technology.
And this is normal and it's how technology works. Bitcoin is the gateway to other cryptocurrencies now, therefore it will be strong for now but as soon as other exchanges start handling other cryptocurrencies or even better, as soon as people starts getting paid in cryptocurrencies, there won't be a need to buy bitcoin before buying other cryptos, so the marketcap for bitcoin will decrease.