I like the Alice in Wonderland quotes (there's another at the end of the brief). I think the statutory language argument is the clearest path to victory here; i.e., Lautenberg itself contemplates regaining the 2A right upon restoration of civil rights and California automatically restores the right to own firearms after ten years.
That does raise a question. On page 10, paragraph 6, the brief states a state judge ruled that each of the plaintiffs "were entitled to have their pleas withdrawn and the case dismissed." If this is the case, I would think there is no conviction which is required by Lautenberg.
IMO, the argument that the original pleas were not voluntarily and intelligently made because Lautenberg had not yet been enacted is a loser. Before Padilla v. Kentucky (cited in the brief), the federal courts were unanimous that lack of knowledge of collateral consequences of a guilty plea, such as losing the right to vote, did not make a guilty plea invalid. The Supreme Court in Padilla emphasized that the "automatic" deportation Padilla faced was virtually unique and limited its opinion to that issue only. The last I looked, all the lower courts (save one) have read Padilla to apply only where one pleads guilty without knowing he or she would face deportation.
I also do not think Lautenberg is a true ex post facto law because a restriction on the 2A right would likely be considered a civil regulation and not a criminal punishment, much like those pleading guilty to sex offenses before sex offender registration statutes were passed. I believe the U.S. Supreme Court case upholding this is Alaska v. Smith (it's late so I'm going to forgo searching for it).