More / emphasized Rogue-lite could be fun, I wonder if they could take some of the best ideas from their Eurekas and go from there. Like if SE checks out Hades or Dead Cells, making something that has both in the moment wildness (challenge or cheese) and yet also a general sense that each time even with failure is success.
I think really, for all content I want to play, like that idea that even my failures are not a waste of my time. Especially if they're failures that were like "oh, that literally was a waste- thanks..". As an example some of the blue mage carnival was nifty and you had a few ways to do it, but there were a few that were like "IF YOU DONT HAVE THIS SPELL YOU WWWWWWWWIILLLLLL DIE". Yet they don't tell you that, so I would try those a few times and be like "super, cool- literally wasted my time, nothing to show for it".
The magic of a good rogue lite was it gave you the fun of variability with the promise it is also trying to respect your time, and also tend to be a bit more bite sized because of it. If my wife decided it's movie night and I was in the middle of a Hades run honestly I'd just run my character off into death and be like "cool, run done".
Which goes in line with Alleo's comment I think in terms of 'steps', just at least that concept you don't get "well, there goes the value of my time "poof" /wave".
I'd like if they could make a bonus or challenge log so you can make some 'main' progress that way, if you wanted (like your daily roulette bonus).
I feel a memento mori (FFIX) theme'd deep dungeon would be awesome, basically non-stop "our art team is full kite high and making dreams as art" experience lol.
New types of rooms could be nice too, like the grid is helpful for easy design obviously but maybe there will be more shapes (not just how they connect, but how the room itself is). Maybe again look at Hades / Dead Cells, might find rooms that are just rooms for rest or whatever. Perhaps every so often rather than a series of rooms you get an entire floor, like a zone basically. In some ways maybe they could bring Eureka like content and DD together (through DF/PF, solo, you progress DD, then at certain floors you unlock Eureka-scapes that utilize much of the content you've already been earning (you can enter them on demand, don't have to redo the whole DD to get into the 'scape'), some of the lite elements from the DD translating into the scape (so like if you unlocked x items or abilities from DD, like Dead Cells maybe, you can bring those in some way), also adding any "dungeons" like CLL can be instanced to prevent future issues like that). Much easier to progress if you're casual (especially if they put relic into the content), yet there are moments of more Eureka inspired design (unlocked scapes at certain floor, to ensure the floors don't get forgotten can include items in the floors that help you in the scapes). Just to be clear when I say bind some features together I don't mean dying in DD causes mettle loss or whatever lol, I mean you might think of Lost Actions as not being something they make for one content but they can share those neat concepts while also perhaps better bridging the gap between the casual people who want relic and not Eureka and the players who want Eureka and relic, etc, etc.