Currently, the process of resolving duplicate accounts is to find them by accident and search for other duplicate accounts they may have created. It would be nice if an auto-flag was generated for accounts that are potentially duplicates, or if a tool existed that would list accounts that are likely duplicates. This would aid in consolidating multiple unregistered accounts that were created by accident.
If by "duplicate" you mean accounts opened from same machine, you forget shared computers like Internet café or even few family members in the same house. Raising flags for all of those will just create too much noise in my opinion.
If you mean sockpuppet accounts created by same person to earn reputation in illegal ways, there are already scripts to detect that and auto merge/ban such accounts.
All in all, I don't think there's anything to improve or add apart maybe more comfortable mechanism to merge unregistered accounts. (Meaning the user himself can do it)