Once you encrypt the wallet, and print your paper backup, importing the wallet via the paper passphrase will NOT import your previous password. That would be why the paper backup states that anyone with the keys on the paper would have unrestricted access to the wallet.
If you're looking to spend, you would still only require your wallet password as normal.
Armory would still use the blockchain, and so I believe that if it were unsupported you could still use it, but the security holes and what not that could arise would not be patched. Using unsupported software is generally a bad idea, as updates to the Bitcoin protocol may require updates to Armory as well.
I didn't understand your answer.
Here you say:
"That would be why the paper backup states that anyone with the keys on the paper would have unrestricted access to the wallet."
Which sounds like you do NOT need the passphrase only the paper backup to use the wallet, including spending.
Here you say:
"If you're looking to spend, you would still only require your wallet password as normal."
Which sounds like you would need the passphrase to spend.
I don't undserstand, which is the case?
Regarding the last part of your answer, maybe you didn't quite get what I'm asking. What I'm saying is let's say that today I use armory to create a wallet (maybe an offline wallet) and a paper backup. Then let's say I put in a safe box for 5 years. Then when I want to finally retrieve it and spend, let's say armory hasn't been updated in years. Maybe the last version is no longer even compatible with the current releases of bitcoin. How hard is it going to be for me to get access to my coins?
What I'm getting at is I want to make some kind of paper backup that will allow me to easily access the coins even if all the current clients are no longer being kept up to date.
Do you know what I mean?
