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.
yes we also can hope that even the bitcoin will be number one currency, but i think still we cannot say anything about it, because 5 years is really avery big time and anything can happen in this time. I think we can only hope that bitcoin will even continue reaising at that time because bitcoin stiall has very good potential to increase.