"Plausible deniability" is cute, but in practice, who cares?

> impossible to convict someone over it.

Yeah, sure, tell me how well that works for you. "Your honor, the data is mathematically indistinguishable from random bytes so you can't convict me" -> "The witness saw you type in a password to view data from that image, give us the password or you're going to prison. Even if you don't give us the passphrase, the police officer says you might be using something called 'steganography', and that's already enough to convict you"

The court and legal system does not care about clever logical tricks or cryptographic tricks or any of that.