Backup encryption is already out there, even. Time Machine is a very popular solution, and implies a lot of desirable demographics (owns a Mac, set up something about as complicated as a BC wallet, probably has no other backup). So there have been some encryption schemes that stick around silently pending a Time Machine backup and then take out the files there too.

It's pretty hard to say that users "should be safe from this" - most of the solid solutions discussed in this thread are probably used by <5% of people, and maybe much less than that.