I also think that it will be very hard for another crypto currency to replace the position of bitcoin. This is because bitcoin has the longest history in the crypto currency world, known by most people, and have lots of miners, investors and supporters.
If the position is biggest market cap, i think bitcoin can be replaced. Many good coin right now in market and investor must be divide their investment in several investment portfolio. I think as biggest market cap, many coin can compete with bitcoin and it replaceable