I figure several factors will come into play. First, registration has to be completed on April 15, 2014 so the state has an actual count of legal weapons. That would then give them a rough idea of what the financial cost would be to confiscate them at $1000-$1500 per weapon. Originally they were estimating $1 to $1.5 billion based on the conservative assumption there are one million weapons that would be subject to confiscation. Whittle that legal number down significantly through registration and you will probably get a number that is easier to budget for say in the $100 to $150 million range. Remember, unregistered weapons that are seized will not be compensated for since they will be illegal.
Secondly, the legislature will have to be in solid Democrat hands along with the Governor. In fact, a super majority in the Senate, like the Assembly, would give them carte blanche to do what they want.
Third, another horrific incident similar to Sandy Hook anywhere in the United States.
Put those three together and I would lay $1000 in Vegas that confiscation was going to happen.