You need to ask: Who will obtain a gun where they will be registered.
Only the dumbest bad guys.
The mentally disturbed might if their affliction clouds their logical thinking.
Just like outlawing guns will only keep them out of the hands of honest citizens, registering them will only make a list of guns owned by honest citizens. (at least if BIDS is used instead of NICS, no list will be made)
With the current fervor over keeping guns out of the hands of mentally disturbed, and this is favored by portions of the firearms community, this might not be the time that repealing all registration will be feasible. How effective it will be at stopping the mentally disturbed from obtaining firearms is doubtful, but it will still get the list of honest gun owners