Yolen isn't quite inaccessible as Mriaze has a branch from there in his collection, just hard to hide. Which fits Enigma better than restriction IMO. Magic systems doesn't necessarily have to have an Initiation based on behaviour, it just needs to match the Shard's Intent. For example allomancy isn't given to those that preserve things better than others but instead is given to preserve their strength. So agents of Chaos may not need to cause it in order to be Initiated although a magic connected to such an Intent feels like something you can do anywhere regardless of who you are, a bit like Hemalurgy. Why would Chaos insist on a chosen few having its gifts?