Okay, I'm on board for that. However, I don't see any way to avoid the messiness if another state decides they're not obligated to honor Californian civil unions. California can say "all references to 'marriage' shall be construed to mean 'civil union'", or the equivalent, in its own law, but even if DOMA is overturned, a state like Florida can easily say "well, that's a civil union, not a marriage, so it doesn't hold in our state." (FL has no statewide domestic partnership law; certain FL cities and counties do.) Full faith and credit clause notwithstanding, I don't think it's possible to make a state extend full faith and credit toward an institution it doesn't have.

A nationwide "civil unions for all" would work, but making that happen is going to be hard. I'd rather see effort focused that direction than fighting it out in the states, but it's going to be a hell of an uphill battle.