I can see the benefits of per-job ranking "if done correctly" (keywords) but a variety of factors would need to be done before that is put in, such as making maps either random on a per-match basis or making each job generally be good on all maps (i.e. no massive advantages due to specific CCs or job interactions present). Also "how" the reward structure would look like is also important.
Last factor is "do we have the playerbase to sustain this", which at least in my opinion I have strong doubts.
But yeah, hard no on merged queues.
Let's not design around people no-lifing things...