I don't think Altcoins will gain a higher market share than Bitcoin. Although Altcoin has many technologies and applications in practice. However, choosing altcoin to replace BTC is a long way. BTC alone has fought nearly 70% of market capitalization.
Altcoins came intro existence because of bitcoins so yeah they will never be able to match or get close to the market capital being held by bitcoins. I still think that altcoins are good as long as they come in good numbers and come with a solid plan like ethereum and few others.
I prefer trading in bitcoins still because of the solid nature of bitcoins and the price. I know bitcoins price fluctuates a lot but compare with alts and you will get an idea of what I am trying to say. Altcoins are good but only if you have done enough research about the coin and the team behind it.