What happens if an Off list lower becomes onlist?

[bwiese]

Lets say they did bring in new legislation, would the people owning them be grandfathered in?

No one can tell what new legislation could bring in, as it'd be written from scratch.

Given incorporation of RKBA in CA is likely to happen fairly soon, and every gun law will be challengeable at some level and this costs $$$ (combined with a busted budget) I don't see a lot of 'big' new gun laws in CA - maybe just a few more rat-gnawing idiocies being attempted.