If bruteforcing Bitcoins privatekeys is indeed possible then for sure people would really be flocking away into other altcoins in the market considering that security is really at risks or something have the issue.
That may be possible on a bad implementation of the private key generation, theoretically, if it is possible there is a more significant thing to worry about than moving away to altcoins. What made you think if bitcoin private key cryptographic mechanism is compromised or cracked, the other cryptocurrencies are not also technically vulnerable?
Besides, what is the mere importance of the cryptocurrency market compared to say, the banking system, do you think they are utilizing a more stronger and secure technological technique? I don't think so.