Miners will decide. The most profitable chain will be the winner. Doesn't matter what we want. However, if BTC price goes up and we deal with the slow and high transaction fees, then BTC core has a chance since miners will make more with original chain. If 80% of miners are mining B2X, it is going to be a tough win. BTC transactions will take days and high fees if it doesn't have enough miners. If people can't transfer within a few hours then many will be turned off by it.

Many will probably sell BTC to USD and wait. BTC is due for correction anyways. I'd be surprised if BTC pumps post fork.

51% attack will become a concern.

Litecoin, Ether, BCH may even have a chance to take the throne.