Greetings,
By introducing dual bladders, you are trying to solve a problem that shouldn't exist in the first place. In realility, whether you're a dry suit diver or not, the rig should be balanced so you can swim up if your BC fails. Yes, the dry suit can get you up (as can a lift bag), but that's not what they're all about.
By introducing dual bladders, you are introducing more potential failure points that are completely unneeded if you are well balanced. In my opinion, dual bladders are just another gimmick out there that encourage poor diving practices and are supported only by those people and agencies that encourage poor diving practices. These poor diving practices are, in part, what is being referred to when they say "an invitation to disaster".
Example: A "tech" diver in a wet suit + double steels + 3 steel stages + canister light + helmet + a bag full of tools = "invitation to disaster" -- double bladders or not.
Mike