CC is far from dead and it has in fact revived PvP in this game. During most times of the day your queue is going to be less than 5 min even now, when most folks have already got the rank they want for the current patch. If anything, CC has become the gap filler between patches when the rest of the content has been done and folks are waiting on the next one to drop. The addition of series/seasons and the reward track was an excellent addition as well.
The only thing wrong with the Criterion Dungeons was the rewards. The content itself was far from "lazy".
Given that an additional limited job wasn't even mention during the "next 10 years in FFXIV" broadcast, don't bet on another limited job. It's very niche and probably not worth the development resources. At most, we will get Blue Mage "updates" once every expansion cycle. We can probably except something for Blue Mage between 6.4 and 6.5. And I'm perfectly fine with that.
Have you done all 100 floors of the new DD? It's quite literally the best iteration of Deep Dungeon content we have got so far.
In regards to the relic weapon...no one is playing the game "casually" and finishing the relic weapon on multiple jobs in a SINGLE DAY. Maybe the first one, because you were prudent and saved up on tomestones but after that...not a chance.
