[scrupulusalbion]

>what happens when messaging with ciphertext becomes illegal

Back in the late 90s, Ron Rivest proposed Chaffing and Winnowing [0]. In that scheme, no ciphertext is transmitted and therefore no encryption is involved; only plausible plaintext is transmitted. The receiver filters out the chaff, leaving only the intended message. Perhaps one could construct an end-to-end winnow-chaff scheme (E2EWC) to replace existing E2EE schemes.

[0] https://en.wikipedia.org/wiki/Chaffing_and_winnowing

[jcynix]

Technically one can argue it's not encryption. But it wouldn't be that difficult for law makers to add a clause that "any similar method of information hiding" is equal to encryption under this law. E.g. "A donkey is regarded as a horse under this law."