AWB conjecture
Ok, this is not fully baked but I think the general logic is sound.
The Senate bill has no grandfathering of post 94 assault weapons. So you can have a gun that was purchased legally that suddenly becomes illegal with the passage of S2572.
The House similarly had the same issue with their first version of the bill. Leadership there was concerned that this would fail constitutionally and as a result they could lose the entire AWB (discussed later)
The Senate may or may not amend S2572 to address this. If they do not, it seems likely that in conference with the house it will have to get added given that the house leadership understands the need.
Why is no grandfathering a problem for the gun grabbers? You can decide whether the 4th, 5th or 14th amendment applies. Making lawfully acquired property unlawful with the passing of a law without proper compensation (independent of this being about guns) tends to land one in hot water. If/when a federal court decides this is unconstitutional, what can they do? They cannot roll back the law to a previous version. They cannot rewrite the law themselves or otherwise modify it. What they do is strike it down (maybe enjoining it first from enforcement while the parties argue it out). So what are they striking down? MGL 140 131M, the part of MGL that makes it a felony to possess an assault weapon. There goes the entire AWB. Gone. All because they failed to grandfather what we already have.
If I could predict the future, I would have already won Powerball for $1.5B and not still be living in MA. But I do think we will see a grandfather clause before this gets enacted, whether put in by the Senate, the House or when they reconcile.