[mrb]

It takes approximately 2^64 attempts to find a 128-bit collision. The Bitcoin network as a whole--with custom ASICs--computes 2^61 SHA256 compression function calls per second and consumes 150 MW, so it would take it 8 seconds. Or it would take 160 000 secs/44 hours with a single dense rack (7.5 kW) of custom ASICs.

So yeah if you care about the security of a crypto currency, this 2^64 collision attack is very doable and unacceptable. The rule of thumb in crypto is to aim at making attacks cost at least 2^128.