[lxgr]

> The majority of all circulating coins are stored in addresses which have been reused.

Interesting, do you have any statistics on that? But I guess with large exchange wallets, it makes sense.

> only have 80 bits of security against second preimages just by using grover's algorithim

True, but 80 bits are anything but trivial to brute-force using classical computers! I'm not that familiar with quantum complexity, but as I understand it, you'd still need 2^80 quantum operations to brute-force a 160 bit hash.