That's a cool algorithm - and while it does reduce the risk of a hack succeeding I think it still could be considered a 'backdoor'. It's just a backdoor that requires to people to work together to open, harder to compromise yes - but I'd argue still not really secure.

If you have a government entity routinely breaking into companies and taking over access to things (targeting sysadmins) then the scheme doesn't work very well. I think most of the argument behind encryption falls on this idea that it either is secure (no backdoors) or it isn't. You have a spectrum of insecure things you can do that are arguably better than nothing, but they're not secure.