But for a new currency to get traction, it would somehow have to have some kind of unusual advantage over Bitcoin. Maybe a government would outlaw Bitcoin but explicitly commit to not outlawing the new currency. Or maybe there could be some kind of deep flaw discovered in the Bitcoin protocol, and it would be easier for everyone to switch to another, thoroughly tested currency than to fix Bitcoin. Or a new currency could come along with much better properties that for fundamental reasons couldn't be retrofitted into Bitcoin, and that could motivate a switch.
Governments aren't that far behind to just prohibit the use of Bitcoin while other crypto currencies aren't subject to the same law. If governments at some point explicitly prohibit the use of Bitcoin, then they will prohibit crypto in general where all coins will be subject to this law. Otherwise it wouldn't make any sense. That being said, there is nothing that can't be fixed if needed. However, reaching consensus in this case might as well turn out to be a problem since it might even push us closer to alternative sides as XT or Unlimited. They wouldn't mind seeing Core go down as one of them will come out as clear winner.