P.S. My guess is that a lot of the 250 million(!) darkNXT is founder or large early adopter NXT put into "savings" accts, without realizing (or caring) about the "weak" 64 bit security
You forget about probability of huge transfer made accidentally by stakeholder to wrong account number because of NXT Client freeze, like many other users who had such issue before but with less amounts.
I don't think that is a huge issues. The 250m are most likely from people that don't even know that you have to make a transaction to create a public key.
Hell i didn't know until 7 days ago and i have 6 digits of them...