They really just need to decouple SCH from ACN. It is already a job far removed from ACN; it should be a simple matter of copying all its actions and traits to a "new" SCH job. Set the unlock quest to require ACN30 as normal, but give them their own xp bar from that point on. Grandfather all the current SCHs to their current ACN level so they don't lose anything, but require future SCH to level SCH separately from ACN/SMN.