Thorvald of Lym
A Little Sketchy
In sum: The theory proposes the dodecahedron was a component of military cryptology. In addition to providing an aperture for the cipher discs, it was used to seal the dispatches in a way that provided the receiver a quick reference to which cipher applied. Multiple faces meant it could switch between different ciphers easily, such as when communicating over multiple channels, or in the event a cipher was suspected to be compromised.
I'm not familiar with the leading dodecahedron theories, but for someone who got really deep into EnigmaSim a few years ago, it's a very intriguing contender.