"However, even if that was fixed, you still need the previous TxOut scripts in order to execute signing, which have to be retrieved from the blockchain -- again something else that Armory's TxDP structure bundles with it, but a raw unsigned tx from Bitcoin Core does not have."
I think you could make an additional query to the blockchain from bitcoin-core to find this info, AFAIK that is what we are doing now, but the answer to the above question is basically Armory has metadata that has to be fetched while online first, if going from bitcoin-core tx -> Armory tx
etothepi, could you let us know what exactly that info is?
https://github.com/bitcoin/bips/blob/master/bip-0010.mediawikiWith multi-sig coming, that whole message format changed, and BIP 10 is obsolete. But at least right now, everything you need to know is there. It's "draft" because I was the only one doing offline tx and no one wanted to contribute to making a standard out of it.
The new version for multi-sig also natively handles offline tx (it's just a 1-of-1 "multi"-sig). I'll document it once design flux settles down.