Although another coin could replace bitcoin, this happeining anytime soon is pretty unlikly id say. If millions of people end up putting money into bitcoin either to use or as an investment its goin to take something pretty serious to convince them to try what at the end of the day is just some alt coin. Bitcoin is cryptocurrency. there can be only one!! (main one)
Yep the top 20 already contains better coins than bitcoin or with better features, yet bitcoin still owns 97% of the total altcoin market share.
So that replacement either will never come or it will take many years, and give people a fair chance to switch to the new coin in time.