At the moment there's currently TWO late game missions people do to earn money and resources, along with the DLC for capitalizing on extra Eternal Orbs found... and it's kind of a problem when it comes to keeping players interesting...
Aside from Dreams and Nightmares, all of the other missions after Vanaduke pale in comparison to rewards. Even when it comes to just having an alternate place to earn Radiants it would be nice to have a larger variety of missions that are also just fun to do.
I really like the concept of Breaking in the Recruits, sort of a return to the surface and some non-story focused task... even if it later turned into more story focused stuff.
So here's a couple of ideas to help this:
First would be the ability to replay old missions with a depth boost... enemies inside change to match what you would fine in that stratum, and it would change on a daily basis. When it comes to exactly which ones you'd of course leave out the missions talking with the NPCs and I'd also suggest leaving out the stuff prior to Squire Rank and some of the tutorial themed missions.
Next would be changing Danger Missions to end one floor further down, you can use this as an opportunity to have more lore added to the game, but you can also toss in a few boxes and remove a few from the treasure floor, overall still keeping the number of boxes the same, just with the treasure floor being deeper.
Last would simply be more missions, it doesn't have to be for lore, it can literally just be for fun. As long as the deepest depth is 28 then you have something players can enjoy that isn't Firestorm Citadel.
personally i'd love to have many of the non-random arcade levels made always-available as replayable stratum 6 optional missions! a lot of these are cool and fun but only rarely accessible through the arcade and not very rewarding.
stratum 5 missions already exist for Jigsaw Valley, Concrete Jungle and Dark City (The Rotting Metropolis is one of my favorite missions to replay for fun sometimes, i love the region), but it'd also be nice to see these for Starlight Cradle(!), Scarlet Fortress, and Aurora Isles - preferably featuring all of their possible floors, and in stratum 6. and yeah, i could also see versions of the boss levels scaled up to tier 3 being added alongside them! (maybe a mission with a couple random floors and then a guaranteed Treasure Vault at the end to make the new content a little more prominent! adjusted for its presence in a mission of course, with the skip elevator removed and probably some reduced treasure boxes so it's not significantly more rewarding than other missions. just to have an accessible treasure mimic fight)
maybe, since OCH is now free and there'll probably never be another DLC expansion, all these optional missions could be held in OCH's shelf of the missions menu? preferably these scaled-up level sets would always be accessible! but yeah, it'd make sense to also have some kind of daily incentive to do specific missions too, maybe one of these optional missions could be highlighted daily or cloned into prestige missions with some kind of extra reward for clearing it once