In my opinion it's very unlikely that BitcoinCash(BCH) will kick out Bitcoin(BTC) out of the first spot. Theoretically possible, but very unlikely. Even so, if BitcoinCash(BCH) were to beat Bitcoin(BTC), I'm sure it wouldn't happen after the Segwit2x fork. It would take lots of lots of years of convincing people to use BitcoinCash(BCH).