How does having people import their private key make it any easier to calculate the coins due to them? The coins due for each account should be calculated when the snapshot occurs and doesn't require user input so I don't see why a script that securely enables users to provide evidence of ownership and provide an address to receive their coins is any different. You still need to calculate the coins that are due to each account either way. Infact it would be easier to not store every address on your chain and instead have a script that looks at your snapshot data when they go to claim their coins and then sends the correct allocated amount from a pool of redemption coins that is entirely automated removing trust altogether from the system. Plus this way you could keep the redemption system going for far longer and if you wanted have it send you 1% to your address which can be documented on the blockchain this way