Quantum computers aren't a magic bullet. Yes using Shor's algorithm the search speed can be increased exponentially however at what cost? For example say once ASICs become mainstream the cost to attack/defend the network using ASICs is $20,000 per TH.....
I think the "magic bullet" of quantum computing, concerning bitcoin, would be used against ECDSA. AFAIK, if you manage to build one in secret, you could start stealing some bitcoin addresses secretly.
But still, I believe the devs will have the time to change the pubkey algorithm before such threat becomes a reality.