It is inevitable that technology will constantly become better and faster. This means security will jee to buff up to keep up with the power of the latest technology that could be used to crack security. I guess when quantum computing becomes a threat to bitcoin that all miners will move to it too and then there will not be a problem since the bitcoin network s made of many quantum computers and their added power will be very difficult to stop so it will be plenty secure. As far as private keys go the same will happen.