From a brief Googling leading to Winlink's web site, it sounds like Winlink isn't even encrypted at all [1]:
> Q260 While monitoring transmissions from WL2K stations, I notice that the content appears as “gibberish”. Isn’t this illegal?
> A260 The content looks that way because it is a compressed binary format called "B2F." This format is available to anyone, so the compressed data is not considered encryption or illegal for radio amateurs.
Is the concern that people are encrypting Winlink payloads anyway? And wouldn't this already be illegal under current rules?
[1] https://www.winlink.org/sites/default/files/wl2k_faq_2015031...
(Edit: formatting)