The only real other cryptocurrency poised to exchange Bitoin, r rather surpass it in market cap we ought to say, is Ethcoeum. The only reason behind this is on the basis that hundreds of companies depend on ETH to run their company, where as Bitcoin is more so of the individualized expense type of factor for many.re
it will be the forever hope for the other cuurencies that they will replace bitcoin. bitcoin is now very strong crypto currency in the world market. it has the highest value in the market than all other crypto currecies. the rising rate of the bitcoin is also very high. the security is a plus point that bitcoin is. Other crypto currencies can hope only that they will replaced the king ''BITCOIN".
In short run, I don't think bitcoin will be defeated by altcoins. In long run, bitcoin will still dominate coin market, but its strength will be decreased by altcoins I guess.