Bitcoin is the boss of all virtual currencies and nothing can replace bitcoin, now we have ETH and ETC from the team and i dont know the reason for two coins ,i expect more splits from them,they may or may not do it.
For the time being, it is the boss of all the digital coin. But it might be replaced by ZCash or Ethereum.
If the block size of the bitcoin is increased to 2MB or higher in the next 6 months, it will still be the Number one.