Alright, guys, we're getting close to an actual release here. I wanted to bump this topic again so we can resume this discussion and find an appropriate solution.
We will support ARC::Data.load and ARC::Data.dump for our own format and load_data will do the same thing that RMXP does. This is for script compatibility.
As for the encrypted format, we will use the .arc format for the data which is used by the editor and we will call the encrypted version .arc as well. Files names will not be changed, only the extension will be changed.
If we can pull it off anyhow, we should try to generate a huge encryption key based on something the userdeveloper gives us. e.g. he could give us his name and we use a hashing function to generate some badass key that will be used to encrypt his game individually. The question is only how we can pull this off since we have to add that key somehow into the game so the engine knows what to use to decrypt the data. Or should we use one key? Because if we allow a different key, updates for any games would require the user to enter the same string for the key generation which might not be such a good idea. Except, of course, if the encryption key generation string becomes a project setting that is saved so the user can compile his game with the same encryption key as much as he wants.