Gold has never been replaced as a store of value and probably never will be by another look alike product. So i dont think BTC will ever be second, but other Altcoins will be used for everyday shopping or to use Ethereum platform or Lisk platform etc. World needs more than one digital coin.
I agree with you on the latter, but i see it is a bit of an unfair to compare gold and Bitcoin in this instance. Since Bitcoin could have an technical issue one day and lose a lot of its value, while another crypto might be just fine and surpass Bitcoin. This can not happen with gold. Gold could only crash if we found new cheap ways to create it or find a big and unexpected amount. So i see Bitcoin failing as the more likely scenario of those two.