I feel retainer ventures were meant to fill the need for new gathering classes. Combat retainers can be sent out to gather almost any hide, tooth, or claw that you can obtain from the open world. This could be expanded of course but adding a Skinner class or Salvager would feel redundant at this current point. Adding in new crafters would necessitate rebalancing who gets what recipe and would just cause more problems than its worth. And as others have said, existing features already fulfill some of those perceived gaps (we can desynth and meld already). I'd personally like something new that mimics the Monster Rearing from FFXI but tied into the Companion system so we could raise monsters to fight alongside us, killing two birds with one stone by scratching that beastmaster itch.