A "manual" approach is already available: using the public blockchain snapshot or a backup of your own chain (which will be much smaller).
Thanks. I don't like this approach very much because it implies some centralization - even if it's not likely that it can be abused as XCN isn't suitable for "timestamping" purposes (like Factom). For now, I would prefer to export my transactions every week.
Part of the information is already saved in the wallet, we could eventually try to add the missing information so the user doesn't see an incomplete transaction data.
I wonder how much bigger the wallet file would become, though.
That would be the approach I would favour. Maybe a separate file can be added so the wallet file isn't cluttered with transaction data?
In the end it's just your blockchain data. Everyone's different because it starts collecting full tx data a couple weeks before your first use. You could backup it along with the wallet (i.e. blocks/ and trie.dat, with wallet.dat).