Hasn't the solution to this problem always been easy? Just encrypt before you type it into imessages; this applies to _all_ untrusted communication channels. Don't tell me base64-encoding/decoding is what's stopping you from having perfect security?
Exactly, if you're dealing with truly sensitive information where any leak is unacceptable, make your own encrypted blob. Don't trust any communication software to do it for you.
The concern typically isn't backdoors, it's bugs. I've had plenty of terrible experiences with Enigmail.
