I think going forward they should get rid of the whole "2 sub-classes for each job." It only restricts our ability to customize. We already saw this happen when they added rogues, but no other job could cross-class any ROG skills. Goad would've been a great cross-class skill for Bards and other DoW's, but because Square is strictly adhering to the 2 sub-classes for each jobs, no one could make use of it.
Instead, Square should go down a list, ability by ability, and determine which jobs can cross-class it, whether for balance or lore reasons. Don't want DoW's having access to Cure/Physick/Stoneskin? Then simply don't allow it to be cross-classed by any DoW except for Paladins. If Raging Strikes is deemed too OP for monks, they can just disallow that individual ability, while still allowing other Bard abilities to be cross-classed.
